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ELEMENTS OF MECHANICAL ENGINEERING [15EME14 / 24]

Department of ME, ACE CHETHAN B S

MODULE – 1

ENERGY RESOURCES Energy Resources: Non-renewable and renewable energy resources, Petroleum based

solid, liquid and gaseous fuels, Calorific values of fuels, Combustion and combustion

products of fuels, Solar Power: Solar Radiation, Solar constant (definition only), Solar

Thermal energy harvesting, ex: liquid flat plate collectors, solar ponds (principle of

operation only), Solar photovoltaic principle. Wind Power: principle of operation of a

typical windmill. Hydro Power: Principles of electric power generation from hydropower

plants, Nuclear Power: Principles of Nuclear power plants, Bio Fuels: introduction to

bio fuels, examples of various biofuels used in engineering applications, Comparison of

biofuels with petroleum fuels in terms of calorific value and emission. Steam Formation

and Properties: Classification of boilers, Lancashire boiler, Babcock and Wilcox

boiler, boiler mountings and accessories (No sketches for mountings and accessories), wet

steam, saturated and superheated steam, specific volume, enthalpy and internal energy.

Energy Resources: energy is defined as the capacity to do work.it is primary requirement

for day to day activities of human beings.

ENERGY- Capacity to do work.

- Most of the energy that we use is mainly derived from conventional energy sources.

- Due to the vast demand of energy, the rate of depletion of these resources has reached

alarmingly low levels.

- This situation has directed us to seek alternate energy sources such as solar, wind,

ocean, biomass, Hydel etc.

ENERGY SOURCES:

The energy existing in the earth is known as CAPITAL energy.

Energy that comes from outer space is called CELESTIAL or INCOME

energy.

The CAPITAL energy sources are mainly, fossil fuels, nuclear fuels and heat traps.

CELESTIAL ENERGY SOURCES ARE- Electromagnetic, gravitational and particle

energy from stars, planets, moon etc.

ELECTROMAGNETIC ENERGY of the earth’s sun is called DIRECT SOLAR

ENERGY. This results in WIND, HYDEL, GEOTHERMAL, BIOFUEL, etc.

GRAVITATIONAL ENERGY of earth’s moon produces TIDALENERGY.

RENEWABLE SOURCES OF ENERGY:

Energy sources which are continuously produced in nature and are essentially

inexhaustible are called renewable energy sources.



1. Direct solar energy 2. Wind energy

3. Tidal energy 4. Hydel energy

5. Ocean thermal energy 6. Bio energy

7. Geo thermal energy 8. Peat

9. Fuel wood 10. Fuel cells

11. Solid wastes 12. Hydrogen

NONRENEWABLE ENERGY SOURCES:

Energy sources which have been accumulated over the ages and not quickly replenish

able when they are exhausted.

1. Fossil fuels.

2. Nuclear fuels.

3. Heat traps.

ADVANTAGES OF RENEWABLE ENERGY SOURCES:

1. Non exhaustible.

2. Can be matched in scale to the need and can deliver quality energy.

3. Can be built near the load point.

4. Flexibility in the design of conversion systems.

5. Local self-sufficiency by harnessing locally available renewable energy.

6. Except biomass, all other sources are pollution free.

DISADVANTAGES OF RENEWABLE ENERGY SOURCES:

1. Intermittent nature of availability of energy such as solar, wind, tidal etc. is a major

setback in the continuous supply of energy.

2. Solar energy received at the earth is dependent on local atmosphere conditions, time

of the day, part of the year etc.

3. Sources such as wind, tidal etc. are concentrated only in certain regions.

4. Technology is not fully developed to meet the present energy requirements.

5. Systems such as solar cells require advanced technologies and hence costlier.

6. Application to transport sector has been found to be not viable as on today.

ADVANTAGES OF NON-RENEWABLE ENERGY SOURCES:

1. Initial cost are lower. Hence widely used.

2. Unit power costs are much lower and so are economical



3. Sources are highly reliable.

4. Power generation technologies are well established.

DISADVANTAGES OF NON-RENEWABLE ENERGY SOURCES:

1. The sources are getting depleted and soon will be exhausted.

2. They pollute the atmosphere.

3. They are not freely available.

Petroleum based Fuels:

Formed mainly from ancient microscopic plants and bacteria that lived in the ocean and

salt water seas. These micro-organisms died and settled to the sea floor, they mixed with

sand silt to form organic rich mud which was gradually heated and compressed chemically

transforming into petroleum. The liquid petroleum gases which are less dense than water

move upwards through earth’s crust. It passes through an impermeable layer of rock which

traps the petroleum creating a reservoir of petroleum and natural gas.

Types of Fuels: - The important fuels are as follows-

1) Solid fuels, 2) Liquid fuels & 3) Gaseous fuels

Solid fuels

Coal is the major fuel used for thermal power plants to generate steam.

Coal occurs in nature, which was formed by the decay of vegetable matters

buried under the earth millions of years ago under pressure and heat.

This phenomenon of transformation of vegetable matter into coal under earth’s crust is known as Metamorphism.

The type of coal available under the earth’s surface depends upon the period of metamorphism and the type of vegetable matter buried, also the pressure

and temperature conditions.

The major constituents in coal moisture (5-40%), volatile matter (combustible & or

incombustible substances about 50%) and ash (20-50%).

The chemical substances in the coal are carbon, hydrogen, nitrogen, oxygen

and sulphur.

In the metamorphism phenomenon, the vegetable matters undergo the transformation

from peat to anthracite coal, with intermediate forms of lignite and bituminous coal.

Liquid Fuels

• All types of liquid fuels used are derived from crude petroleum and its by-products.



• The petroleum or crude oil consists of 80-85% C, 10-15% hydrogen, and varying

percentages of sulphur, nitrogen, oxygen and compounds of vanadium.

• The crude oil is refined by fractional distillation process to obtain fuel oils, for

industrial as well as for domestic purposes.

• The fractions from light oil to heavy oil are naphtha, gasoline, kerosene, diesel and finally

heavy fuel oil.

• The heavy fuel oil is used for generation of steam. The use of liquid fuels in thermal power

plants has many advantages over the use of solid fuels.

Some important advantages are as follows:

1) The storage and handling of liquid fuels is much easier than solid and gaseous fuels.

2) Excess air required for the complete combustion of liquid fuels is less, as compared to the

solid fuels.

3) Fire control is easy and hence changes in load can be met easily and quickly.

4) There are no requirements of ash handling and disposal.

5) The system is very clean, and hence the labour required is relatively less compared to the

operation with solid fuels.

Gaseous Fuels

• For the generation of steam in gas fired thermal plants, either natural gas or

manufactured gaseous fuels are used. However, manufactured gases are costlier than the

natural gas.

• Generally, natural gas is used for power plants as it is available in abundance. The natural

gas is generally obtained from gas wells and petroleum wells.

• The major constituent in natural gas is methane, about 60-65%, and also contains

small amounts of other hydrocarbons such as ethane, naphthenic and aromatics, carbon

dioxide and nitrogen.

• The natural gas is transported from the source to the place of use through pipes, for

distances to several hundred kilometres.

• The natural gas is colourless, odourless and non-toxic.

• Its calorific value ranges from 25,000 to 50,000 kJ/m3, in accordance with the

percentage of methane in the gas.

• The artificial gases are producer gas, water gas coke-oven gas; and the Blast furnace gas.

• Generally, power plants fired with artificial gases are not found.

• The gaseous fuels have advantages similar to those of liquid fuels, except for the

storage problems.



• The major disadvantage of power plant using natural gas is that it should be setup

near the source; otherwise the transportation losses are too high.

Calorific values of fuels:

The calorific value or heat of combustion or heating value of a sample of fuel is defined as

the amount of heat evolved when a unit weight ( or volume in the case of a sample of

gaseous fuels ) of the fuel is completely burnt.

It is usually expressed in Gross Calorific Value (GCV) or Higher Heating Value (HHV) and

Net Calorific Value (NCV) or Lower Heating Value (LHV).

Higher Calorific Value (or Gross Calorific Value - GCV, or Higher Heating Value - HHV) -

the water of combustion is entirely condensed and that the heat contained in the water vapor

is recovered Lower Calorific Value (or Net Calorific Value - NCV, or Lower Heating Value -

LHV) - the products of combustion contains the water vapor and that the heat in the water

vapor is not recovered

Combustion and Combustion Products:

Combustion or burning is the sequence of exothermic chemical reactions between a fuel and

an oxidant accompanied by the production of heat and conversion of chemical species. The

release of heat can produce light in the form of either glowing or a flame. Complete

combustion of fuel is possible only in the presence of an adequate supply of oxygen.

Oxygen (O2) is one of the most common elements on earth making up 20.9% of our

air. Rapid fuel oxidation results in large amount of heat. Solid or liquid fuels must be

changed to a gas before they will burn in their normal state if enough air is present.

Most of the 79% of air (that is not oxygen) is nitrogen, with the traces of

other elements. Nitrogen is considered to be a temperature reducing diluter that must

be present to obtain the oxygen required combustion.

Nitrogen reduces combustion efficiency by absorbing heat from the combustion of

fuels and diluting the flue gases. This reduces the heat available for transfer through the heat

exchange surfaces. It also increases the volume of combustion by products. Which then have

to travel through the heat exchanger and up the stack faster to allow the introduction

of additional fuel-air mixture.

This nitrogen also can combine with oxygen (particularly flame temperatures)

to produce oxides of nitrogen (NOx) which are toxic pollutants. Carbon, hydrogen

and sulphur in the fuel combine with oxygen in the air to form carbon dioxide, water vapour

and sulphur dioxide, releasing 8084 kcals, 28922 kcals and 2224 kcals of heat

respectively. Under certain conditions, carbon may also combine with the oxygen to

form carbon monoxide, which results in the release of smaller quantity of heat (2430

kcals/kg of carbon). Carbon burned to CO2will produce more heat per unit of fuel than CO or

smokes are produced.



SOLAR POWER PLANT

Solar radiation is radiant energy emitted by the sun from a nuclear fusion reaction that

creates electromagnetic energy. The spectrum of solar radiation is close to that of a black

body with a temperature of about 5800 K. About half of the radiation is in the visible short-

wave part of the electromagnetic spectrum.

Solar Constant Isc:

This is the amount of energy received in unit time on a unit perpendicular to the suns

direction at the mean distance of the earth from the sun. The surface of the earth receives

about 1014kW of solar energy from the sun. One square meter of the land exposed to direct

sun-light receives an energy equivalent of about 1.353 kW of power. This constant may

increase by only 0.2 percent at the of each 11 year solar cycle. The radiant solar energy falling on

the earth surface is directly converted into thermal energy. The surfaces on which the solar

rays fall are called collectors.

Insolation:-Insolation is the amount of solar radiation reaching the earth. Also called

Incident Solar Radiation. Maximum value is 1000 kW/m2.

Components of Solar Radiation:

Direct radiation

Diffuse radiation

Reflect radiation

Solar Thermal Energy harvesting:

Radiant solar energy is directly converted into thermal energy (heat energy) by using

a collector. This process is called as Helio thermal process. The surface on which the solar

rays fall is called a collector. The collector may be either flat plate collector or focussing

collector.

There are two types of collectors:

(a) Flat plate collectors (b) Focusing collectors.



LIQUID FLAT PLATE COLLECTORS:

It has the following components:

(a) Absorbing plate –

Made of Copper, Aluminium or steel.

It is coated with material to enhance the absorption of solar radiation.

From the absorbing plates heat is transferred to tubes which carry either water or air.

(b) Water tubes –

These are metallic tubes through which water circulates. Which are attached to the

absorber plate.

(c) Transparent covers –

• Sheets of solar radiation transmitting materials placed above the absorbing plate.

• They allow solar energy to reach the absorbing plate while reducing

convection, conduction and re-radiation heat losses.

• Made of a toughened glass, usually 4mm thick. Which helps in reflecting the incident

solar energy back to the absorber plate.

• Glass cover permits the entry of solar radiation as it is transparent for incoming short

wave lengths.

(d) Insulation –

• It minimizes and protects the absorbing plate from heat losses.

Working – Sun’s rays falling on the transparent covers are transmitted to the absorbing

plate. The absorbing plate usually of Cu, Al or galvanized iron is painted dead black



for maximum absorption. The collector (plate) will absorb the sun energy and transfer it to

the fluid in the pipe beneath the collector plate.

Use of flat mirrors on the sides improves the output. Water from the overhead tank is

made to flow through the water tubes. Solar rays passes through the transparent cover and

falls on the absorber plate. Heat energy from the absorber plate is transferred to the cold

water flowing through the tubes. Worm water rises above the cold water because of low

density and flows into the heater tank.

SOLAR POND TECHNOLOGY:

• A salinity gradient solar pond is an integral collection and storage device of solar

energy.

• By virtue of having built-in thermal energy storage, it can be used irrespective of time and

season.

• In an ordinary pond or lake, when the sun's rays heat up the water this heated water, being

lighter, rises to the surface and loses its heat to the atmosphere.

• The net result is that the pond water remains at nearly atmospheric temperature.

• The solar pond technology inhibits these phenomena by dissolving salt into the bottom

layer of this pond, making it too heavy to rise to the surface, even when hot.

• The salt concentration increases with depth, thereby forming a salinity gradient.

• The sunlight which reaches the bottom of the pond remains entrapped there.

• The useful thermal energy is then withdrawn from the solar pond in the form of hot brine.

The pre-requisites for establishing solar ponds are: a large tract of land (it could be barren),

a lot of sun shine, and cheaply available salt (such as Sodium Chloride) or bittern.

• Generally, there are three main layers. The top layer is cold and has relatively little salt

content.

• The bottom layer is hot -- up to 100°C (212°F) -- and is very salty.



• Separating these two layers is the important gradient zone.

Solar pond electric power plant:-

• The energy obtained from a solar pond is used to drive a Rankine cycle heat engine.

• Hot water from the bottom level of the pond is pumped to the evaporator where the working

fluid is vaporized.

• This vapour then flows under high pressure to the turbine where it expands and work thus

obtained runs an electric generator producing electricity.

• The vapour is then condensed through a cooling system and the liquid is pimped back to the

evaporator and the cycle is repeated.

Application of solar ponds:-

A. Heating and cooling of buildings.

B. Production of power

C. Industrial process heat.

D. Heating animal housing.

E. Drying crops on farms.

PHOTOVOLTAIC CELL:

Solar energy can be directly converted to electrical energy by means of photovoltaic

effect. Photovoltaic effect is defined as the generation of an electromotive force

(EMF) as a result of the absorption of ionizing radiation. Devices which convert



sunlight to electricity are known as solar cells or photovoltaic cells. Solar cells are

semiconductors, commonly used are barrier type iron-selenium cells.

• Iron-selenium cells consist of a metal electrode on which a layer of selenium

is deposited.

• On the top of this a barrier layer is formed which is coated with a very thin layer of

gold.

• The layer of gold serves as a translucent electrode through which light can impinge

on the layer below.

• Under the influence of sunlight, a negative charge will build up on the gold

electrode and a positive charge on the bottom electrode.

• This difference in charge will produce voltage in proportion to the suns radiant

energy incident on it.

Basic photovoltaic system for power generation:

This system consists of the following:

1. Solar array (solar cells) 2. Blocking diode 3. Battery storage 4. Inverter 5.

Switches and load centre

• In the solar cell array due to photovoltaic effect electrical power (D.C.) will

be produced in proportion to the suns radiant energy incident on it.



This generated power will be stored in the battery storage.

• A blocking diode ensures that the battery would not discharge power back to solar

array during the period when there is no sunlight.

• An inverter converter converts the D.C power to A.C. and sends it to the load centre.

• From the load centre A.C. power is distributed accordingly with the help of switches.

WIND ENERGY:

Wind energy is the energy contained in the force of the winds blowing across the

earth surface. Wind energy is defined as the kinetic energy associated with the

movement of large masses of air over the earth’s surface.

The circulation of the air in the atmosphere is caused by the non-uniform heating of

the earth’s surface by the sun. The air immediately above warm area expands and becomes

less dense. It is then forced upwards by a cool denser air which flows in from the surrounding

areas causing wind.

Power in the wind:

Wind possesses kinetic energy by virtue of its motion. Any device capable of slowing

down the mass of moving air, like a sail or propeller, can extract part of this energy and

convert into useful work.

The kinetic energy of one cubic meter of air blowing at a velocity V is given by,



E = 1/2ρV2 J/m

2

In one second, a volume element of air moves a distance of V m. The total volume

crossing a plane, one square meter in area and oriented normal to the velocity vector in one

second is therefore v m3

The rate at which the wind energy is transferred, i.e., wind power is given by,

P = EV

= 1/2ρV2

W/m2

No device, however well designed can extract all the wind energy because the wind

would have to be brought to halt and this through the rotor. It has been found that for

maximum power output the exit velocity is equal to one-third of the entrance velocity. Thus a

maximum of 60% of the available energy in the wind is converted into mechanical energy.

A windmill is the oldest device built to convert the wind energy into mechanical

energy used for grinding, milling and pumping applications. It consists of a rotor fitted with

large sized blades.

Merits:

1. The wind is free and with modern technology it can be captured efficiently.

2. Once the wind turbine is built the energy it produces does not cause greenhouse

gases or other pollutants.

3. Many people find wind farms an interesting feature of the landscape

4. Remote areas that are not connected to the electricity power grid can use wind

turbines to produce their own supply.

5. Wind turbines have a role to play in both the developed and third world.

6. Wind turbines are available in a range of sizes which means a vast range of people

and businesses can use

De-merits:

1. Wind turbines are noisy.



2. The strength of the wind is not constant and it varies from zero to storm force.

3. Only selected places it can be harnessed.

4. Hydro Power Plants: 5. In hydroelectric power plants the potential energy of water due to its high location is

converted into electrical energy. The total power generation capacity of the

hydroelectric power plants depends on the head of water and volume of water flowing

towards the water turbine.

6. 7. The hydroelectric power plant, also called as dam or hydro power plant, is

used for generation of electricity from water on large scale basis. The dam is

built across the large river that has sufficient quantity of water throughout the

river. In certain cases where the river is very large, more than one dam can built

across the river at different locations. The rain water flowing as river can be stored

behind dams and released in a regulated way to generate hydro power.

8. Working Principle of Hydroelectric power plant

9. The water flowing in the river possesses two type of energy:

10. (1) The kinetic energy due to flow of water and

11. (2) Potential energy due to the height of water.

12. In hydroelectric power and potential energy of water is utilized to generate electricity

the formula for total power that can be generated from water in hydroelectric power

plants due to its height is given.

13. The potential energy of water stored at a height is converted into mechanical energy

in water turbine. The mechanical energy produced by the water turbine is converted

into electrical energy. After doing useful work water is discharged from the turbine to

the river through a water to the tail race through a draft tube.

14. Merits: - environmental friendly source, large scale power generation, energy at free

of cost.



15. Demerits: - expensive to build the dam, summer water may not sufficient to produce

electricity.

NUCLEAR POWER:-

Nuclear energy is the energy that holds the nucleus of an atom. The energy released during

nuclear fission or fusion, especially when used to generate electricity.

Nuclear Fission: - Nuclear fission is the process of splitting a nucleus into two nuclei with

smaller masses. Fission means “to divide”.

“The most common nuclear fuels are 235U. Not all nuclear fuels are used in fission

chain reactions”

Chain Reaction: - A chain reaction is an ongoing series of fission reactions. Billions of

reactions occur each second in a chain reaction.

On earth, nuclear fission reactions take place in nuclear reactors, which use controlled

chain reactions to generate electricity.

Uncontrolled chain reactions take place during the explosion of an atomic bomb.

Nuclear Fusion: - Nuclear fusion is the combining of two nuclei with low masses to form

one nucleus of larger mass. Nuclear fusion reactions are also called thermonuclear reactions.

Working principle of a nuclear power station

The schematic diagram of nuclear power station is shown in A generating station in which

nuclear energy is converted into electrical energy is known as nuclear power station.



The main components of this station are nuclear reactor, control rods, steam generators,

steam turbine, coolant pump, feed pump, condenser, cooling tower.

NUCLEAR REACTOR:- A nuclear reactor is a device in which nuclear chain reactions are

initiated, controlled, and sustained at a steady rate, as opposed to a nuclear bomb, in which the chain

reaction occurs in a fraction of a second and is uncontrolled causing an explosion.

CONTROL RODS: - Control rods made of a material that absorbs neutrons are inserted into the

bundle using a mechanism that can rise or lower the control rods. The control rods essentially contain

neutron absorbers like, boron, cadmium or indium.

STEAM GENERATORS: - Steam generators are heat exchangers used to convert water into steam

from heat produced in a nuclear reactor core. Either ordinary water or heavy water is used as the

coolant.

STEAM TURBINE: - A steam turbine is a mechanical device that extracts thermal energy from

pressurized steam, and converts it into useful mechanical. Various high-performance alloys and super

alloys have been used for steam generator tubing.

COOLANT PUMP: - The coolant pump pressurizes the coolant to pressures of the order of 155bar.

The pressure of the coolant loop is maintained almost constant with the help of the pump and a

pressurizer unit.

FEED PUMP: - Steam coming out of the turbine, flows through the condenser for condensation and

recirculated for the next cycle of operation. The feed pump circulates the condensed water in the

working fluid loop.

CONDENSER: - Condenser is a device or unit which is used to condense vapor into liquid. The

objective of the condenser are to reduce the turbine exhaust pressure to increase the efficiency and to

recover high quality feed water in the form of condensate & feedback it to the steam generator

without any further treatment.

COOLING TOWER: - Cooling towers are heat removal devices used to transfer process

waste heat to the atmosphere. Water circulating through the condenser is taken to the cooling tower

for cooling and reuse The reactor of a nuclear power plant is similar to the furnace in a steam

power plant. The heat liberated in the reactor due to the nuclear fission of the fuel is taken up

by the coolant circulating in the reactor. A hot coolant leaves the reactor at top and then

flows through the tubes of heat exchanger and transfers its heat to the feed water on its way.

The steam produced in the heat exchanger is passed through the turbine and after the work

has done by the expansion of steam in the turbine, steam leaves the turbine and flows to the

condenser. The mechanical or rotating energy developed by the turbine is transferred to the

generator which in turn generates the electrical energy and supplies to the bus through a

step-up transformer, a circuit breaker, and an isolator. Pumps are provided to maintain

the flow of coolant, condensate, and feed water.



ADVANTAGES:-

Nuclear power generation does emit relatively low amounts of carbon dioxide (CO2).

The emissions of greenhouse gases and therefore the contribution of nuclear power plants to

global warming is therefore relatively little.

This technology is readily available, it does not have to be developed first.

It is possible to generate a high amount of electrical energy in one single plant.

DISADVANTAGES:-

The problem of radioactive waste is still an unsolved one.

High risks: It is technically impossible to build a plant with 100% security.

The energy source for nuclear energy is Uranium. Uranium is a scarce resource, its supply is

estimated to last only for the next 30 to 60 years depending on the actual demand.

Biofuels

Introduction: - Biomass is biological material derived from living, or recently living

organisms. It most often refers to plants or plant-derived materials which are specifically

called lignocelluloses. As an energy source, biomass can either be used directly via

combustion to produce heat, or Indirectly after converting it to various forms of biofuel.

This biomass may be transformed by physical, chemical and biological processes to

biofuels. In chemical forms biomass is stored solar energy and can be converted into solid,

liquid and gaseous energy carries. Biomass is biological/organic material derived from



living, or recently living organisms. (The term is equally applicable to both animal and

vegetable derived material, but in the context of energy, it refers to plant based material)

The term ‘Biofuel’ refers to liquid or gaseous fuels for the transport sector that

are predominantly produced from biomass. A variety of fuels can be produced from

biomass resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-

Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The biomass

resource base for biofuel production is composed of a wide variety of forestry and

agricultural resources, industrial processing residues, and municipal solid and urban

wood residues.

A. Renewable energy source and Stored in form of complex organic compounds of

Carbon, Hydrogen, Oxygen and Nitrogen etc.

B. It is a source of ‘5F’: food, fodder, fuel, fibre and fertilizer.

C. It can be converted into useful forms of energy through different conversion routes.

D. Gets converted into fossil fuels after several million years under certain

conditions of pressure, temperature, air etc. fossil fuels are not renewable, hence, are

not biomass.

Source of biomass: - sources of biomass/biofuels are:-

Examples of various biofuels used in engineering applications: - The various bio-fuels are

bio-methanol, bio-ethanol, bio-diesel, bio-gas and producer gas.

First-generation biofuels are made from sugar, starch, vegetable oil, or animal fats

using conventional technology. The basic feedstock for the production of first-

generation biofuels come from agriculture and food processing.

The most common first-generation biofuels are:

Biodiesel: Extraction with or without esterification of vegetable oils from seeds

of plants like soybean, oil palm, oilseed rape and sunflower or residues including

animal fats derived from rendering applied as fuel in diesel engines.



Bioethanol: Fermentation of simple sugars from sugar crops like sugarcane or

from starch crops like maize and wheat applied as fuel in petrol engines.

Bio-oil: Thermo-chemical conversion of biomass. A process still in the development

phase.

Biogas: Anaerobic fermentation or organic waste, animal manures, crop residues an

energy crops applied as fuel in engines suitable for compressed natural gas.

Second-generation biofuels are derived from non-food feedstock including

lignocellulose biomass like crop residues or wood. Two transformative technologies are

under development.

6CO2 + 6H2O (CH2O)6 + 6O2 + 636 kCal

(biomass)

Sunlight

Chlorophyll t

• Biochemical: Modification of the bio-ethanol fermentation process including a pre-

treatment procedure

• Thermo chemical: Modification of the bio-oil process to produce syngas and

methanol, Fisher-Tropsch diesel or dimethyl ether (DME).

Emission of bio-fuels: - Biodiesel plays a vital role in reducing emission of many air

pollutants. The emission of carbon monoxide (CO), sulphur oxides (SOx), nitrogen oxides

(NOx) etc.., is lesser than those of petroleum fuels and thus these are eco-friendly.

Calorific value of bio-fuels: - Calorific values of biofuels will be considerably lesser than that of

petroleum fuels.

Advantages of biomass energy:-

Renewable and inexhaustible (theoretically) source of energy.

Biomass is very abundant.

It is easy to convert to a high energy portable fuel such as alcohol or gas which are

efficient, viable and relatively clean-burning.

It is cheap in contrast to the other energy sources.

Biomass production can often mean the restoration of waste land (e.g. deforested

areas).

Commercial use of biomass may reduce the problem of waste disposal.

It may also use areas of unused agricultural land and provide jobs in rural

communities.

When direct combustion of plant mass is not used to generate energy (i.e.

fermentation, pyrolysis, etc. are used instead), there is minimal environmental impact.



Disadvantages of biomass energy:-

A dispersed and land-intensive source.

Low energy density.

Could contribute a great deal too global warming and particulate pollution if directly

burned.

Still an expensive source, both in terms of producing the biomass and converting it to

alcohols.

On a small scale there is most likely a net loss of energy- energy must be put in to

grow the plant mass.

Comparison of biofuels with petroleum fuels in terms of calorific value and emission:

It is well known that petroleum diesels are the major source of air pollutions

that create an adverse impact on human health and overall greenhouse gases. Biodiesel has

some great benefits over petroleum diesel, such as it produces 4.5 units of energy

against every unit of fossil energy and also it has some environment-friendly properties such

as it is non-toxic, biodegradable and safer to breathe. Biodiesel is also a clean-burning and

stable fuel. Properties of biodiesel such as oxygen content, cetane number, viscosity,

density and heat value are greatly dependent on the sources (soybean, rapeseed or

animal fats) of biodiesel. Engine performance and emissions depend on the properties of

biodiesels. Biodiesel is a highly oxygenated fuel that can improve combustion

efficiency and can reduce unburnt hydrocarbons (HCs), carbon dioxide (CO2), carbon

monoxide (CO), sulphur dioxides (SO2), nitric oxide (NOx) and polycyclic aromatic HC

emissions.

However, brake-specific fuel consumption slightly increases. Popularity of biodiesel

as renewable sources of alternative fuel of petroleum diesel is growing quickly due to

increased environmental awareness and the rising price of diesel. It is an earth-friendly

choice of consumers that already occupies a great volume of the world's fuel sector due to its

clean emission characteristics.

Steam Formation and Properties:

Introduction: - All the substance under suitable conditions of temperature and pressure can

exist in one of the three states via solid, liquid or gas. But water is one of the pure substance

that exists in all the three phases namely in solid phase as ice, liquid phase as water and

gaseous phases as vapour (steam).

Most of the practical problems in thermal engineering are concerned with

liquid and gaseous phase rather than the solid phase. Water, which is liquid at normal



temperature begins to boil to form steam when heat sufficiently. In practice, steam is

generated in steam generators or popularly known as BOILERS.

Definition of Steam: Steam can be defined as it is a mixture of water and air or it can also be

defined as vapour of water.

Formation of steam at constant pressure:

Consider 1 kg of water at 00C taken in a cylinder, on which a constant pressure P is exerted.

Point A on the temperature-enthalpy graph.

When this water is heated its temperature rises till the boiling point is reached. This

temperature is called saturation temperature (Ts). Point B on the graph.

Further addition of heat, initiates the evaporation of water while the temperature

remains at saturation temperature until all of water is converted into steam. Point C on the

graph.

On heating the steam further, it increases the temperature of steam above the saturated

temperature to superheated steam.

1. Saturation temperature (Ts): It is defined as the temperature at which the water

begins to boil at constant pressure.



2. Sensible heat (hf): It is the amount of heat required to raise the temperature of 1 kg of

water from 00C to the saturation temperature (boiling point) at constant pressure. It is also

known as enthalpy of the liquid.

3. Latent heat of evaporation (hfg): It is the amount of heat required to evaporate 1 kg of

water at saturation temperature to 1 kg of dry steam at the same saturation

temperature at constant pressure. Also known as enthalpy of evaporation.

4. Enthalpy of superheat: The amount of heat required to increase the temperature of dry

steam from its saturation temperature to any desired higher temperature at constant pressure

is called enthalpy of superheat.

STATES OF STEAM: - The steam as it is being generated can exist in 3 states as wet

steam, dry saturated steam and superheated steam.

• Wet Steam: It is defined as a two-phase mixture of entrained water molecules and

steam at saturation temperature.

• Dry Steam (dry saturated steam): As wet steam is heated further, the water molecules in

the steam get converted into vapour. Dry steam is the steam at saturation temperature having

no water molecules in it. Point C.

• Superheated Steam: It is defined as the steam which is heated beyond its dry state to

temperatures higher than its saturated temperature at the given pressure.

Dryness fraction of steam: A wet steam has different proportions of water molecules and

dry steam. Hence, the quality of wet steam is specified by the dryness fraction which

indicates the amount of dry steam in the given quantity of wet steam and is denoted

by x. It is defined as the ratio of mass of dry steam in a given quantity of wet steam to the

total mass of wet steam.

It is defined as the ratio of mass of dry steam in a given quantity of wet steam to the total

mass of wet steam.

Let mg = mass of dry steam

mf = mass of water molecules

Dryness fraction, x= mg/ (mg+mf)

• The dryness fraction of wet steam is less than 1.

• The dryness fraction of dry steam is 1



ENTHALPY (h), kJ/kg: It is the amount of heat required to raise the temperature of 1 kg of

water from 00C to the desired form of steam at constant pressure. It is the sum of the internal

energy and work done at constant pressure.

Enthalpy of Dry Saturated Steam (hg):It is the amount of heat required to raise the

temperature of 1 kg of water from 00C to 1 kg of dry saturated steam at constant

pressure.

ℎg= ℎf + ℎfg KJ/Kg

Enthalpy of Wet Steam (h): It is the amount of heat required to raise the temperature of 1

kg of water from 00C to 1 kg of wet steam to the specified dryness fraction, at

constant pressure.

ℎ = ℎf+ xℎfg KJ/Kg

Enthalpy of Superheated Steam (hsup): It is the amount of heat required to raise the

temperature of 1 kg of water from 00C to 1 kg of superheated steam to the stated

saturated steam temperature, at constant pressure. It is the sum of enthalpy of dry steam and

the amount of superheat.

hsup=hg+Cps(Tsup-Ts) KJ/Kg

hsup=hf+hfg+Cps(Tsup-Ts) KJ/Kg

Where Cps is the specific heat of superheated steam.

Steam Properties:

• Ice melts.

• Water is heated beyond boiling point.

• Steam is defined as vapour of water.

• Vaporization. Gaseous phase.

• Steam is two phase mixture of water and steam.

The important properties of steam are

1. Pressure 4. Enthalpy

2. Temperature 5. Internal energy

3. Specific volume 6. Entropy

Specific volume (m3 /kg): It is the volume occupied by the unit mass of a substance.



Specific Volume of Dry Saturated Steam (Vg): It is the volume occupied by 1 kg of dry

saturated steam at a given pressure.

Specific Volume of Wet Steam (v): It is the volume occupied by 1 kg of wet steam to the

specified dryness fraction at a given pressure. v = xvg

Internal Energy of Steam: The total heat energy of a dry saturated steam at a constant

pressure is the sum of the sensible heat and latent heat. But in latent heat a portion is used for

external work. Therefore, the actual energy stored in the steam is the sensible heat and the

internal latent heat. This actual energy stored in the steam is called internal energy of steam.

It is defined as the difference between the enthalpy of the steam and the external work of

evaporation.

Steam boilers:

Definition of boilers:

• Boiler is defined as a closed metallic vessel in which the water is heated beyond the boiling

state by the application of heat liberated by the combustion of fuels to convert it into steam.

Function of a boiler:

• The function of the boiler is to supply the steam at the required constant pressure with its

quality either dry or as nearly as dry, or superheated. The steam can be supplied from

the boiler at a constant pressure by maintaining the steam generation rate and the steam flow

rate.

CLASSIFICATION OF BOILERS:

According to the circulation of water and hot gases:-

a) Fire Tube boilers:-In fire tube boilers the hot flue gases produced by the combustion

of fuel passes through the tubes which are surrounded by water.

Eg: - Cornish boilers, locomotive boilers, marine boilers and Lancashire boiler.



b) Water Tube boilers: - In water tube boilers water circulated inside the tubes, while the

hot gases produced by the combustion of fuels pass around the tubes.

Eg: - Babcock and Wilcox boiler, Stirling boilers…etc.

According to the location of furnace.

a. Internally fired boilers: - If the furnace is situated inside the boiler shell, the boiler is

called internally fired boilers. Most of the fire tube boilers are internally fired.

b. Externally fired boilers:-If the furnace is situated outside the boiler shell, the boiler is

called externally fired boilers. Water tube boilers are always externally fired.

According to the circulation of water.

I. Natural circulation: - In these boilers, water is circulated by natural convection

currents that are set up due to the temperature difference.

II. Forced circulation: - water is circulated with the help of pump driven by a motor.

Forced circulation is used only in high pressure and high capacity boilers like La

mont boilers and Benson boilers, etc...

According to the axis of the shell.



a) Vertical boilers: - axis of the boilers shell is vertical. Ex:-Cochran boilers.

b) Horizontal boilers:-axis of the boilers shell is horizontal. Ex:-Babcock &Wilcox

boilers, Lancashire boilers.

According to their uses.

1) Stationary boilers

2) Locomotive boilers

3) Marine boilers, etc…..

BABCOCK & WILCOX BOILER:

It is a horizontal, externally fired, natural circulation, water tube boiler.

It consists of mainly four parts:

(a) Steam and water drum – It is filled with three-fourths water. It stores the feed water

and steam.

(b) Water tubes – number of water tubes are connected through downtake header and

uptake header in which water circulates as shown in fig.

(c) Baffle plates- it is placed across the water tubes .it deflect the hot gases coming out

from the furnace to allow the hot gas pass around water tubes.

(d) Internal furnace– it burns the coal to produce hot flue gases.

(e) Super heater – it is set of U-tubes just below the boiler drum, it converts the steam

into superheated steam.



Working: - Water is introduced into the boiler drum through the feed valve. Water descends

into the down take headers, into the water tubes and then into the uptake headers. The hot

flue gases from the furnace pass over the water tubes. The path of the hot gases is guided by

the baffle plates as shown in the fig., and passes out to the chimney. As the hot gases pass

over the water tubes, the water gets converted into steam. This steam due to low density rises

up the tube through the uptake headers and reach the top of boiler drum. This sets up a

natural circulation of water. The steam collected in the boiler is wet. This is made to pass

through the super heater U-tubes just below the boiler drum. The hot gases on their way

out pass over these tubes hence converting the steam into superheated steam. The

superheated steam in then passed out to the turbine through the steam stop valve. For safety

the boiler consists of safety valve, steam stop valve, blow-off pipe, and pressure gauge, etc.

Lancashire boiler:

It is a horizontal, internally fired, natural circulation, fire tube boiler.

• This boiler consists of a large horizontal cylindrical shell placed on the brick wall.

Two large flue tubes are placed inside the shell, which carry the hot flue gases.

• The boiler shell is filled with water to three-fourths of its volume and the remaining space is

the steam space.



• Hot flue gases from the combustion are made to pass through the flue tubes.

• In the first run it passes from the front end to the rear end of the boiler.

• At the rear end they are made to pass to the bottom central channel.

• In the bottom central channel the hot gases travel from rear end to the front end of the

boiler. This is the second run.

• At the front end the hot gases enter into side channels 1 and 2 and travel to the rear end of

the boiler. This is the third run.

• At the rear end hot gases coming out of channels 1 and 2 are made to exit to the

chimney through the rear exit passage.

• During the first, second and third pass the heat transfer takes place between hot flue gases

and the water in the shell, converting water into steam.

• The steam gets accumulated in the steam space at the top.

• Super heater (set of U-tubes) is placed at the rear end of the shell.

• For safety the boiler consists of safety valve, steam stop valve, blow-off valve,

pressure gauge, etc.

BOILER MOUNTINGS AND ACCESSORIES:

MOUNTINGS:

1) Water level indicator: It indicates the level of water in the boiler drum.



2) Pressure gauge: Indicates the pressure of the steam in the boiler.

3) Safety Valves: When the pressure inside the boiler drum exceeds the desired level, the

safety valves blows off the excess steam from the boiler.

4) Steam stop valve: It regulates the flow of steam from the boiler.

5) Feed check valve: It checks the level of water in the boiler drum.

6) Blow off valve: Its function is to remove periodically the sediments and impurities

collected at the bottom of the boiler.

7) Fusible plug: It is a device used to extinguish the fire in the furnace.

ACCESSORIES:

1. Economizer: The function of an economizer is to heat the feed water, before being

supplied to the boiler, using the products of combustion (flue gas) discharged from the boiler.

2. Air preheater: The function of an air preheater is to preheat the air being supplied

to the furnace for combustion.

3. A super heater: is a device used to convert saturated steam or wet steam into dry steam.

4. Feed pump: pumps the water into the boiler at high pressure.

5. Steam separator: it is used to separate the water particles is present in the steam before

enters the turbine or engines.

6. Steam trap: it is used to drain off the condensed water accumulated in the steam pipes and

steam separator without allowing the escape of high pressure steam from it.



Sl

no WATER TUBE BOILERS FIRE TUBE BOILERS

1. In water tube boilers, water is

circulated inside the tubes and hot

gases surround the water tubes

In fire tube boilers, hot gases pass

inside the tube and water surrounds

the tubes.

2. Furnace is situated outside the

boilers shell.

Furnace is situated inside the boiler

shell

3. Water circulates between the drum

and the tubes maintaining a closed

circuit.

Water circulates within the boilers

drum only.

4. Combustion space is large,

complete combustion of fuel is

possible

Combustion efficiency is low.

Combustion takes place in a small

space within the boiler shell.

5. Steam generation rate is fast. Steam generation rate is slow

6. Evaporating capacity is high Rate of evaporation is low

7. Thermal efficiency is high Thermal efficiency is low

8. All parts of water tubes boilers are

easily accessible for cleaning,

inspection and repair

Cleaning, inspection and repairing is

difficult due to inaccessible parts.

9. High cost Low cost

10. Used in power plants Used in process industries.



MODULE – 2

TURBINES AND IC ENGINES AND PUMPS

STEAM TURBINES

Turbines and IC Engines and Pumps: Steam turbines – Classification, Principle of

operation of Impulse and reaction turbines, Delaval’s turbine, Parson’s turbine. (No

compounding of turbines). Gas turbines: Classification, Working principles and Operations

of Open cycle and closed cycle gas turbines. Water turbines- Classification, Principles

and operations of Pelton wheel, Francis turbine and Kaplan turbine. Internal

Combustion Engines: Classification, I.C. Engines parts, 2 Stroke and 4 stroke Petrol

engines, 4 stroke diesel engines. PV diagrams of Otto and Diesel cycles. Problems on

indicated power, brake power, indicated thermal efficiency, brake thermal efficiency,

mechanical efficiency, and specific fuel consumption, [numericals on IC Engines]

----------------------------------------------------------------------------------------------------------------

PRIME MOVER: Prime mover is a self-moving device which converts the available natural

source of energy into mechanical energy of motion to drive the other machines. The various

types of prime movers which convert heat energy produced by the combustion of fuels into

mechanical energy.

Eg: Turbines, Internal combustion Engines, External combustion Engines, etc……

Turbine: A turbine can be defined as a power producing machine. The device

generates power by converting the kinetic energy of a stream of fluid (such as water,

steam, or hot gas) into mechanical energy (in the form of rotation of shaft) through the

principles of impulse and reaction. Turbines are used to drive electro generators to produce

electricity and pumps to supply fluid flow in a hydraulic system.

Turbines are classified based on the medium used to run the rotors of turbine:

1) Steam turbine – The steam is used to run the turbine.

2) Gas turbine – Here the gases of the burnt fuel is used to run the turbine.



3) Water Turbine – Here the water is used as a medium to run the turbine.

EXPANSION OF STEAM IN THE NOZZLE:

A nozzle is a passage of varying cross-section through which steam flows.

Figure shows a convergent-divergent nozzle in which the cross-sectional area of the

nozzle diminishes from the entry to throat, and thereafter diverges to the exit as shown in

the figure. Steam is expanded in a nozzle to increase its kinetic energy. The high pressure and

low velocity steam generated in a boiler enters the nozzle, and as it passes between the entry

and the throat, the pressure of the steam drops to a lower value. In other words, steam

expands to a low pressure. This drop in pressure reduces the enthalpy (heat content) of

steam.

Since there is no external work and heat transfer in the nozzle, the

reduction in the enthalpy of steam must be equal to the increase in velocity (kinetic energy)

of the steam. In other words, the steam performs work upon itself by accelerating itself to a

high velocity. Hence, the steam comes out of the nozzle with low pressure, and high

velocity. Beyond the throat, the nozzle diverges to a certain length, so as to allow any

incomplete expansion of the steam to take place.

PROPELLING FORCE IN THE STEAM TURBINE:

The high pressure steam is made to pass through a nozzle. The steam expands in the nozzle

i.e. its pressure falls & the heat energy is converted into kinetic energy which makes the

steam to flow with a greater velocity. This high velocity steam enters the rotating part of the

turbine & undergoes a change in direction of motion which gives rise to a change of

momentum & therefore a force. This constitutes the driving force of the turbine.



STEAM TURBINES

A steam turbine is defined as a prime mover that converts the heat energy of

the steam into mechanical energy in the form of rotary motion. Finally the rotary motion is

used to generate electricity in the generator. It is used for driving electric generators, ship

propellers, pumps, fans, compressors, etc.

Steam turbines are mainly classified into two types:--

1. Impulse Turbine (De-Laval Turbine): In impulse turbine the steam expands in

nozzles and its pressure does not alter as it moves over the blades.

2. Reaction Turbine (Parson’s Turbine): In reaction turbine, the steam expands

continuously as it passes over the blades and thus there is a gradual fall in the pressure during

expansion.

1) IMPULSE TURBINE (DE-LAVAL TURBINE)

The turbine consists of a series of curved blades fixed on the circumference

of a single wheel called rotor. The rotor in turn is connected to a shaft as shown in fig a.



In operation, the high pressure, low velocity steam generated in a boiler is made to

flow through a convergent-divergent nozzle. As the steam passes through the nozzle,

expansion takes place and the pressure of the steam decreases.

This drop in pressure of the steam results in the increase in the velocity (kinetic

energy) of steam. The change in pressure and velocity of steam is shown in figure b. The

high velocity jet of steam coming out of the nozzle is directed towards the moving

blades of the turbine.

The steam flowing over the blades undergoes a change in its velocity and

direction thereby resulting in change of momentum. The force due to the change of

momentum is the impulse force that acts in the direction normal to the blades, thereby

pushing the blade in its direction. The force acting on the blade is shown in figure b. Since a

number of blades are fixed on the wheel, each blade comes in contact with the high velocity

jet of steam. As a result, the wheel rotates continuously at high speeds. Hence, the shaft

connected to the rotor also rotates. Thus, the kinetic energy of steam is converted into

mechanical work. The output (rotation) at the shaft can be utilized for driving

generators to produce electricity, or any other devices.

Important note on Impulse turbine:

1. Since all the kinetic energy is absorbed by one row of the moving blades only, the speed

of the wheel is too high varying from 25000 to 30000 rpm. Such a high speed produces

large centrifugal forces, increases vibration, causes over heating of the bearings, etc., and this

makes it impossible for direct coupling to other machines.

2. Loss of energy due to higher exits velocity of steam.



2) REACTION TURBINE (PARSON’S TURBINE)

Reaction turbine was invented by Sir Charles Parson and hence widely called

Parson's turbine. The turbine runs by the reactive force of the jet of steam, rather than the

direct push or impulse as is in the case of impulse turbine Figure a shows the arrangement of

blades in a reaction turbine & the change in pressure and velocity of steam. Reaction turbine

consists of alternate rows of fixed and moving blades. The fixed blades are fastened

(fixed) to a stationary casing and hence the name, while the moving blades are

mounted on the periphery of a rotating wheel called rotor. The rotor in turn is

connected to a shaft.

In reaction turbines, there are no nozzles. Instead, the blades are designed in such

way that, the spaces between the blades have the shape of a nozzle. Hence in

reaction turbines, pressure drop takes place gradually and continuously over both the

moving and fixed blades. Pressure velocity graph shown in figure. Also, the blades used

in reaction turbines are asymmetrical in shape being thicker at one end. In operation, the

high pressure, low velocity steam generated in a boiler passes over the first row of fixed

blades. The space between the fixed blades acts as nozzle due to which the steam gets

expanded to a low pressure and high velocity. The fixed blades guide the high velocity jet of

steam to move on to the moving blades.

The high velocity jet of steam now glides over the moving blades where it

undergoes a change in its velocity and direction, thereby resulting in change of momentum.

This gives impulse force to the blade and hence the rotor to rotate. Thus the kinetic energy of

the steam is converted into mechanical energy of rotation of the rotor. Also, the steam while

passing through the moving blades suffers further drop in pressure, as the moving blades too

act as nozzles. When the steam leaves the moving blade, a reactive force is set up. Thus, the

net force acting on the moving blade is the impulse force of the incoming steam and the



reactive force of the outgoing steam. For this reason, reaction turbines are also called as

impulse-reaction turbine.

The process continues in the next row of fixed and moving blades. Thus, the steam

expands and does work on the blades causing the rotor to rotate at high speeds. Hence, the

shaft connected to the rotor also rotates, thereby doing useful work.

Difference between IMPULSE and REACTION steam turbines:

Impulse turbine Reaction turbine

Turbine blades have symmetrical profile Turbines blades have aero-foil profile

The steam completely expands in the

nozzle and its pressure remains constant

during its flow through the blade passage

The steam expands partially in the fixed

blade (nozzle) and further expansion takes

place in the rotor (moving) blades

The pressure on both ends of the moving

blade is same

The pressure on two ends of the moving

blades are different

Less efficient More efficient

High speed and requires less space Comparatively less speed and requires

more space

Suitable for small power requirements Suitable for medium and higher power

requirements

Advantages of steam turbines over other prime movers:

a) Steam turbines can work at high temperatures and very high steam pressures.

Hence the thermal efficiency is higher compared to other prime movers.

b) Steam turbines are rotary engines and hence do not have any reciprocating parts.

Hence, less vibration and noise.

c) No wear and tear of the parts. Also lubrication is not required.

d) Turbine rotor can be balanced accurately.

e) Power generation in a steam turbine is at a uniform rate. Hence, a flywheel is not

required.

f) Higher speeds with greater speed range is possible.

g) Steam turbines can take considerable over-load with only a slight reduction in its

efficiency.

h) Steam turbine can be designed in sizes ranging from a few kW to over 1000

MW in a single unit. This enables to use steam turbines as prime movers in large

power plants.

i) Steam turbines are extensively used to propel ships of high tonnage and also

to drive high speed generators, compressors, etc.



GAS TURBINES

A gas turbine is a thermal prime mover that converts the heat energy of the hot air or

burnt gases into mechanical work in the form of rotation of shaft.

Based on the flow of the working substance during the cycle of operation, gas

turbines are classified into two types:

Open cycle gas turbine: In the open cycle gas turbine, the working fluid is the atmospheric

air and the heat rejection process occurs in the atmosphere as the turbine exhaust is

discharged into the atmosphere.

Closed cycle gas turbine: In the closed cycle gas turbine the heat rejection process is

accomplished in a heat exchanger and the same working fluid is cycled continuously. The

working fluid does not come in contact with the product of combustion.

1) Working of an OPEN CYCLE GAS TURBINE

Figure shows the line diagram of an open cycle gas turbine. It consists of a rotary

compressor, combustion chamber, and a turbine (reaction type). Both the turbine and the

compressor are mounted on a common shaft. This is because, a part of the power

developed by the turbine is required to drive the compressor. In an operation, the

compressor draws air from the atmosphere and compresses it to a high pressure. The

compressed air then flows into the combustion chamber where the fuel is burnt at constant

pressure. The hot gases produced by combustion process mixes with the compressed air. Due

to this, the air gets heated up and also its mass increases.

The high-pressure and high-temperature hot gases are then made to flow through the

turbine blades, where in the heat energy is converted into mechanical work, in much the

same way as in the case of steam turbines. The shaft of the turbine may be connected to a

generator for producing electricity. The gases coming out from the turbine are discharged to

the atmosphere as they cannot be used any more. Since, the working substance is discharged

to the atmosphere, this type of turbine is called as open cycle gas turbine. The working

substance (air and fuel) must be replaced continuously for every cycle of operation.



2) Working of a CLOSED CYCLE GAS TURBINE

Figure shows the line diagram of a closed cycle gas turbine. It consists of a

rotary compressor, heater, a turbine (reaction type) and a cooler. The compressor and

the turbine are mounted on a common shaft. In a closed cycle gas turbine atmospheric air or

some other stable gases like argon, helium, nitrogen, carbon dioxide, etc., may be used as the

working fluid.

In operation, the working fluid is compressed to a high pressure in a compressor r and

then passed to a heater where it is heated with the help of some external source. The working

fluid will not come in contact with the products of combustion as in the case of open

cycle gas turbine. Instead, heat is transferred using a heat exchanger.



The high-pressure and high-temperature fluid is then made to flow through the

turbine blades, where in the heat energy is converted into mechanical work in much the

same way as in the case of steam turbines. From the turbine the fluid is passed to a cooler,

where it is cooled to its original temperature from external cooling source.

The low-temperature and low-pressure fluid from the cooler is then passed to the

compressor for the next cycle to take place. Since the working fluid is circulated again and

again, this type of turbine is called closed cycle gas turbine.

Difference between closed and open cycle gas turbines:

Sl no OPEN CYCLE CLOSED CYCLE

1 Fresh working fluid enters in every

cycle

Working fluid is continuously

circulated in every cycle of operation

2 The working fluid after doing work

is exhausted to the atmosphere.

The working fluid after doing work is

cooled and fed back to the compressor

for the next cycle.

3 There is mass transfer along with

heat and work transfer.

Only heat and work transfer take place

between the system and the

surrounding.

4 Only atmospheric air is used as the

working fluid.

Any fluid with better thermodynamic

properties can be used as working fluid.

5 The compressed air mixes with the

products of combustion of fuel, the

mass of the compressed air increases.

The compressed fluid is heated by an

external source. Hence the mass of the

fluid remains same.

6 Since the compressed air gets

contaminated with product of

combustion of fuel, turbine blades

are subjected to corrosion and

erosion.

Since, there is no contamination of the

working fluid, corrosion and erosion of

the turbine blades is avoided.

7 Comparatively lower due to pressure

losses

Higher efficiency

8 Comparatively less Installation and maintenance costs are

high

9 Comparatively less Weight of the turbine per KW power

developed is high.



WATER TURBINES

A water turbine is a hydraulic prime mover that converts the energy of falling

water into mechanical energy in the form of rotation of shaft. The mechanical energy in turn

is converted into electrical energy by means of an electric generator.

Water turbines are classified based on the following factors:

Type of energy available at the inlet of the turbine:

(a) Impulse turbine: The energy available at the inlet of the turbine is only kinetic energy.

Example: Pelton wheel, Girad turbine, Banki turbine, etc.

(b) Reaction turbine: Both pressure energy and kinetic energy is available at the inlet of the

turbine.

Example: Kaplan turbine, Francis turbine, Thomson turbine, etc.

Based on the head under which turbine works:

a) High head turbine: Head of water available at the inlet of the turbine ie, above

300 m. Example: Pelton wheel.

b) Medium head turbine: Head of water available at the inlet of the turbine ranges from 50

m to 150 m. Example: Francis turbine.

c) Low head turbine: Head of water at the inlet will be less than 50m. Example: Kaplan

Turbine.

Based on the direction of flow of water through the runner:

a) Tangential flow turbine: Water flows along the tangent to the runner. Example: Pelton

wheel.

b) Axial flow turbine: Water flows in a direction parallel to the axis of rotation of the

runner. Example: Kaplan turbine.

c) Radial flow turbine: Water flows in a radial direction through the runner. Radial

flow turbines are further classified into inward radial flow and outward radial flow

turbines. Example: Thomson turbine, Girad turbine, Old Francis turbine.

d) Mixed flow turbine: Water flows racially into the runner and leaves axially, Example:

Modern Francis turbine.



1) PELTON WHEEL TURBINE

Pelton wheel is a tangential flow impulse turbine, used for high heads and small

quantity of water flow. Figure shows the schematic diagram of a Pelton wheel. The Pelton

wheel consists of the following parts: nozzle with spear head, shaft, rotor, buckets, casing,

and tailrace.

Working:

In operation, water from the reservoir (dam) having potential energy flows

through the penstock and enters the nozzle. As water flows through the nozzle, the potential

energy of water is completely converted into kinetic energy in the nozzle. The high velocity

jet of water issuing from the nozzle impinges on the curved blades fixed around the runner

wheel. The impulse force due to the high velocity jet of water sets the runner wheel into

rotary motion. Hence, the shaft coupled to the runner wheel also rotates thereby doing useful

work. Thus, the potential energy of the water is converted into mechanical work. After

performing work, the water freely discharges to the tailrace. The work produced at the output

shaft is used to drive a generator to produce electricity the electricity is then transmitted

to a substation where transformers increase voltage to allow transmission to homes,

office, and factories.

Advantages:

1) Simple in construction and easy maintenance.



2) To drive more power multiple jets (2 to 6) Pelton wheel may be used.

Disadvantages:

1) A lot of head loss occurs when the river discharge is low.

2) FRANCIS TURBINE

Francis turbine is a mixed flow reaction turbine used for medium heads. It was

the first Hydraulic turbine with radial flow, designed by American scientist James Francis.

Figure shows the front and top views of a Francis turbine. Francis turbine consists of the

following parts: spiral casing (volute), runner, shaft, guide blade (fixed blade), guide

wheel, moving blade (runner blade).

Working:

In operation, water from the reservoir (dam) flows through the penstock and

enters the spiral casing. As the water flows through the tapered spiral casing, a part of its

potential energy is converted into kinetic energy. Water flows through the guide blades, gets

deflected and then flows radially inwards to the outer periphery (outer diameter) of the

runner. The water then moves over the moving blades in the radial direction and is finally

discharged to the tailrace axially from the centre of the runner via a draft tube.

During its flow over the runner blades, the blade passages act as nozzle, and the

remaining part of the potential energy is converted into kinetic energy. It is important to note



at this point, that the jet of water does not impinge on the runner. In fact, they are leaving the

runner at high velocity. So, the momentum is converted into force as in the case of

impulse turbine. Since the water leaves the blades at high velocity, there is a reaction force

on the runner. This force sets the runner into rotary motion. Hence the shaft connected to

the runner also rotates thereby doing useful work. The shaft in turn drives the generator to

produce electricity.

Advantages:

1) No head loss occurs even at low discharge of water.

Disadvantages:

1) Eddy losses are more

2) Since the spiral casing is grounded, runner is not easily accessible. Hence

dismantling is difficult.

3) KAPLAN TURBINE

The Kaplan turbine is a low head reaction turbine in which water flows axially,

Figure shows the rotor and front view of a Kaplan turbine. Kaplan turbine consists of the

following parts: guide vanes, runner vanes, shaft, spiral casing, tailrace, hub, and blade.



Working:

Kaplan turbine is an axial flow reaction turbine and is used where large quantity of

water is available at low heads. The turbine consists of a hub or boss fixed to a vertical shaft.

The runner blades attached to the hub are adjustable, and can be turned about their axis to

take care of change of load. The runner has only 4 to 8 blades. Similar to Francis turbine,

Kaplan turbine also has a ring of fixed guide blades at the inlet to the turbine. The inlet is a

scroll shaped tube surrounding the fixed blades. In operation, water from the reservoir

flows through the penstock and enters the spiral casing. A part of the potential energy of

water is converted into kinetic energy in the spiral casing.

The water then moves through the guide blades (fixed blades), gets deflected and

then flows axially through the runner blades as shown in figure. During its flow over the

runner blades, the blade passages act as nozzle, and the remaining part of the potential energy

is converted into kinetic energy. The water leaves the runner blades at high velocity, and as a

result, a reaction force is set up causing the runner to rotate at high speeds. Hence the shaft

connected to the runner also rotates thereby doing useful work. The shaft in turn drives the

generator to produce electricity. The water discharging at the centre of the runner enters the

draft tube whose end is immersed into the tailrace as in Francis turbine.

Advantages:

1) Simple in construction and requires less space.

2) Eddy losses are almost eliminated.

Disadvantages:

1) Cavitation is likely to occur due to high velocity flow of water.

Difference between impulse water turbine and reaction water turbine:

SI

No.

Reaction Water Turbine Impulse Water Turbine

1. Reaction turbines are used for low and

medium heads. Example Francis and

Kaplan turbine.

Impulse turbines are used for high heads.

Example Pelton turbine

2. Pressure drop occurs in both fixed and

moving blades.

No pressure change occurs at the turbine blades

3. Part of the pressure energy is converted to

kinetic energy in the spiral casing, and the

remaining in the blade passages that acts as

nozzle.

Pressure energy is completely converted to

kinetic energy in a nozzle.

4. Reaction turbines rotate faster given the

same head and flow conditions.

Comparatively low.



5. Reaction turbines require more

sophisticated fabrication because of the use

of larger and more intricately profiled

blades and casings.

Comparatively ease in fabrication.

6. Reaction turbines must be encased to

contain the water pressure (or suction), or

they must be fully submerged in the water

flow.

Relatively not necessary

Difference between Francis and Kaplan turbine:

Sl

no

Francis turbine Kaplan turbine

1 It is a mixed flow turbine It is an axial flow turbine

2 Medium head turbine, requires

medium quantity of water

Low head turbine, requires large quantity of water

3 Number of guide vanes are around 16

to 24

Number of guide vanes are around 3 to 8

4 The runner is supported by a driving

shaft

The runner is the extension of the vertical shaft

5 Guide vanes are assembled with the

help of links and levers to act as valves

Guide vanes are made adjustable for smooth flow of

water. They are so designed and fixed around the

hub

6 Requires large space Requires less space due to sloped vanes

7 Eddy losses are impossible to avoid It is almost eliminated

8 Cavitation do not occurs Cavitation is likely to occur

9 Draft tube is of simple elbow type Draft tube is of circular to rectangular type

ENGINE:

A heat engine is a machine, which converts heat energy into mechanical energy. The

combustion of fuel such as coal, petrol, and diesel generates heat. This heat is supplied to a

working substance at high temperature. By the expansion of this substance in suitable

machines, heat energy is converted into useful work.

Heat engines can be further divided into two types:

(i)External combustion and (ii) internal combustion.

External combustion Engine: - In a steam engine the combustion of fuel takes place

outside the engine and the steam thus formed is used to run the engine. Thus, it is known as

external combustion engine.



Internal combustion Engine: - In the case of internal combustion engine, the

combustion of fuel takes place inside the engine cylinder itself.

I C ENGINE:

An internal combustion engine (I C Engine) is a heat engine, which converts the heat

energy released by the combustion of the fuel taking place inside the engine cylinder into

mechanical work.

The advantages of I C Engines compared to External combustion Engines are high

efficiency, light weight, compactness, easy starting, suitable for mobile applications and

comparatively lower initial cost.



CLASSIFICATION OF I C ENGINES:

According to the type of fuel used: a) Petrol engine - If the fuel used is petrol, the engine is called as petrol engine.

b) Diesel engine - If the fuel used is diesel, the engine is called as diesel engine.

c) Gas engine - gaseous fuels like bio-gas, natural gas, or liquefied petroleum gas (LPG), etc.,

are used as fuels.

d) Bi-fuel (Bio-fuel) engine - these engines use a mixture of more than one fuel. For

example, mixture of diesel and natural gas, mixture of diesel and neem oil, etc.

According to the number of strokes per cycle: a) 4-stroke engine - if the engine completes its working cycle in four different strokes of the

piston, or two revolutions of the crankshaft, it is called as 4-stroke engine.

b) 2-stroke engine - if the engine completes its working cycle in two different strokes of the

piston, or one revolution of the crankshaft, it is called as 2-stroke engine.

According to the method of ignition: a) Spark Ignition (SI) engine - If the fuel is ignited by an electric spark generated by a spark

plug, the engine is called as spark ignition engine.

b) Compression Ignition (CI) engine - In these engines, the fuel ignites when it comes in

contact with the hot compressed air.

According to the cycle of combustion: a) Otto cycle engine - If the combustion of fuel takes place at constant volume, the engine is

called Otto cycle engine.

b) Diesel cycle engine - combustion of fuel takes place at constant pressure.

c) Dual combustion cycle engine - combustion of fuel first takes place partially at constant

volume, and then at constant pressure.

According to the number of cylinders used: a) Single cylinder engine - If the engine consists of only one cylinder, then it is called as

single cylinder engine.

b) Multi-cylinder engine - If the engine consists of more than one cylinder, then it is called as

multi-cylinder engine.

According to the arrangement of cylinders: a) Vertical engine - If the cylinder is arranged in a vertical position, the engine is called

vertical cylinder engine.

b) Horizontal engine - cylinder is arranged in horizontal position.

c) Inline engine - cylinders are arranged in a line. Most trucks are of inline configuration.

d) Radial engine - cylinders are arranged along the circumference of a circle.

e) V-engine - It is a combination of two inline engines equally set at an angle. Passenger

vehicles have V-type configuration.

f) Opposed type engine - cylinders are arranged opposite to each other.

According to the method of cooling: a) Air cooled engine - If the heated cylinder walls (due to combustion of fuel) are cooled by

circulating air, the engine is called air cooled engine.



b) Water cooled engine - water is circulated through the jacket surrounding the healed

cylinder walls.

According to their uses: a) Stationary engine

b) Automobile engine

c) Marine engine

d) Aircraft engine, etc.

PARTS OF AN IC ENGINE: The following are the main parts of an internal combustion engine.

1) Cylinder 2) Piston

3) Piston rings 4) Connecting rod

5) Crank 6) Crankshaft

7) Crankcase 8) Fly wheel

9) Valves

Cylinder: It is the heart of an I C Engine, as the name indicates is a cylindrical shaped component in

which combustion of fuel takes place. The cylinder is usually made from gray cast iron or

steel alloys in order to withstand the high pressure and temperature generated inside the

cylinder due to combustion of fuel.



Piston: The piston is a close fitting hollow cylindrical plunger moving to and fro in the cylinder. The

power developed by the combustion of the fuel is transmitted by the piston to the crankshaft

through the connecting rod.

Piston Rings:

The piston rings are the metallic rings inserted into the circumferential grooves provided at

the top end of the piston. These rings maintain a gas-tight joint between the piston and the

cylinder while the piston is reciprocating in the cylinder. They also help in conducting the

heat from the piston to the cylinder.

Connecting Rod: It is a link that connects the piston and the crankshaft by means of pin joints. It converts the

rectilinear motion of the piston into rotary motion of the crankshaft.

Crank: The crank is a lever, with one of its end connected to the lower end of the connecting rod,

while the other end connected to the crankshaft.

Crankshaft: The function of the crankshaft is to transform reciprocating motion into rotary motion. The

crankshaft transmits the power developed by the engine through the flywheel, clutch,

transmission and differential to drive (move) the vehicle. The crankshafts are made of carbon

steel.

Crankcase: The crankcase is the lower part of the cylinder block that encloses the crankshaft and

provides a reservoir for the lubricating oil.

Flywheel: It is a heavy wheel mounted on the crankshaft of the engine to maintain uniform rotation of

the crankshaft.

Valves:

The valves are the devices which controls the flow of the intake and the exhaust gases to and

from the engine cylinder. They are also called poppet valves. These valves are operated by

means of cams driven by the crankshaft through a timing gear or chain.



IC ENGINE TERMINOLOGY:

Top Dead Centre (TDC) or Cover end: The extreme position of the piston near to the

cylinder head is called top dead centre. Briefly abbreviated as TDC. In horizontal engines,

like the opposed type engine, the term top dead centre becomes irrelevant, and hence the

term cover end is used in-place of top dead centre.

Bottom Dead Centre (BDC) or Crank end: The extreme position of the piston near to the

crankshaft is called bottom dead centre. Briefly abbreviated as BDC. In horizontal engines,

like the opposed type engine, the term bottom dead centre becomes irrelevant, and hence

substituted by the term crank end.

Bore: The inner diameter of the cylinder is called bore. It is denoted by d.

Stroke or Stroke length: The linear distance travelled by the piston when it moves from top

dead centre to bottom dead centre is called stroke or stroke length. It is denoted by L.

Stroke volume or Swept volume or Piston displacement: The volume swept by the piston

when it moves from the top dead centre to bottom dead centre is called stroke volume or

swept volume or piston displacement. It is denoted by Vs.

Clearance volume: The volume of the cylinder above the top of the piston when the piston

is at the top dead centre is called clearance volume. It is denoted by Vc.

FOUR-STROKE PETROL ENGINE (4-S-P-E):- A four-stroke petrol engine works on Otto cycle. Hence it is also called Otto cycle engine.



The charge used in a 4-Stroke petrol engine is a mixture of air and petrol, and is supplied by

the carburettor in suitable proportions. The charge is ignited by the spark generated by a

spark plug, and for this reason, petrol engines are also called Spark Ignition (SI) engines.

Fig: Otto cycle (P-V diagram)

Working: In a 4-Stroke petrol engine, the working cycle is completed in four different strokes of the

piston.



1) Suction stroke: At the beginning of the suction stroke, the piston is at the top dead centre

(TDC), and is about to move towards the bottom dead centre (BDC). At this instance, the

inlet valve is opened and the exhaust valve is closed. The downward movement of the piston

produces suction (partial vacuum) in the cylinder, due to which fresh charge of air and petrol

mixture is drawn into the cylinder through the inlet valve.

When the piston reaches the BDC, the suction stroke ends and the inlet valve is

closed. With this stroke, the crankshaft rotates through 180° or half-revolution.

The energy required for the piston movement is taken from a battery. The suction of

air takes place at atmospheric pressure, and is represented by the line AB on p-v diagram.

2) Compression stroke: During the compression stroke, the piston moves from BDC to

TDC. Both the inlet and exhaust valves remain closed. As the piston moves upwards, the air-

petrol mixture in the cylinder gets compressed (squeezed), due to which the pressure and

temperature of the mixture increases.

The compression process is adiabatic [Adiabatic - It is a process in which there is no

heat transfer from the system to the surroundings or vice-versa.] in nature and is shown by

the curve BC on p-v diagram. When the piston is about to reach the TDC, the spark plug

initiates a spark that ignites the air-petrol mixture. Combustion of fuel takes place at constant

volume as shown by the line CD on p-v diagram.

Since combustion of fuel takes place at constant volume, 4-Stroke petrol engines are

also called as constant volume cycle engines. With this stroke, the crankshaft rotates by

another 180° or half revolution. The energy required for the piston movement is taken from a

battery.

3) Power stroke (Expansion stroke or Working stroke): During this stroke, both the

valves will remain closed. As the combustion of fuel takes place, the burnt gases expand and

exert a large force on the piston causing it to move rapidly from the TDC to BDC. The force

(or power) is transmitted to the crankshaft through the connecting rod.

As a result, the crankshaft rotates at high speeds. The crankshaft then transmits the

power through clutches, gears, chains, etc... To turn the wheels of the vehicle and cause it to

move. The expansion of gases is adiabatic in nature and is shown by the curve DE on p-v

diagram.

Since the actual power or work is produced by the engine in this stroke, it is also

called as power stroke or working stroke. Also, expansion of gases occurs during this stroke,

and hence the name expansion stroke.

4) Exhaust stroke: Towards the end of the expansion stroke, the exhaust valve opens, while

the inlet valve remains closed. A part of the burnt gases due to their own expansion escapes

out of the cylinder through the exhaust valve.



This drop in pressure at constant volume inside the cylinder is represented by the line

EB on p-v diagram. The exhaust stroke begins when the piston starts moving from the BDC

to TDC. The energy for this stroke is supplied by the flywheel, which it had absorbed in the

previous stroke. As the piston moves upwards, it forces the remaining burnt gases to the

atmosphere through the exhaust valve. The exhaust taking place at atmospheric pressure is

shown by the line BA on p-v diagram.

When the piston reaches the TDC, the exhaust valve closes and the working cycle is

completed. In the next cycle, the piston starts moving from TDC to BDC, the inlet valve

opens allowing fresh charge to enter into the cylinder, and the process continues. Thus it is

clear that, the four different strokes or one working cycle is completed when the crankshaft

rotates through 720° or two revolutions.

Four-stroke petrol engines are commonly used in scooters, motor bikes, cars, large boats, etc.

FOUR STROKE DIESEL ENGINE (4-S-D-E):-

A 4-stroke diesel engine works on Diesel cycle. Hence it is also called Diesel cycle

engine. The working principle is similar to that of 4-stroke petrol engine, except a fuel

injector is used in place of spark plug, and only air enters the cylinder during the suction

stroke and gets compressed in the compression stroke.

Fig: Diesel cycle (P-V diagram)



Working:

1) Suction stroke: At the beginning of the suction stroke, the piston is at the top dead centre

(TDC), and is about to move towards the bottom dead centre (BDC). At this instance, the

inlet valve is opened and the exhaust valve is closed.

The downward movement of the piston produces suction (partial vacuum) in the

cylinder, due to which air from the atmosphere is drawn into the cylinder through the inlet

valve. When the piston reaches the BDC, the suction stroke ends and the inlet valve is closed.

With this stroke, the crankshaft rotates through 180° or half-revolution.

The energy required for the piston movement is taken from a battery. The suction of

air takes place at atmospheric pressure, and is represented by the line AB on p-v diagram.

2) Compression stroke: During the compression stroke, the piston moves from BDC to

TDC. Both the inlet and exhaust valves remain closed. As the piston moves upwards, the air

in the cylinder gets compressed (squeezed), due to which the pressure and temperature of the

air increases.

The compression process is adiabatic in nature and is shown by the curve BC on p-v

diagram. When the piston is about to reach the TDC, a quantity of diesel is injected in the

form of fine sprays into the hot compressed air by a fuel injector.

Combustion of fuel takes place at constant pressure as shown by the line CD on p-v

diagram. Since combustion of fuel takes place at constant pressure, 4-Stroke diesel engines

are also called as constant pressure cycle engines.

With this stroke, the crankshaft rotates by another 180° or half revolution. The energy

required for the piston movement is taken from a battery. Since the heat of compression



ignites the diesel injected into the cylinder, diesel engines are also called as compression

ignition engines.

3) Power stroke (Expansion stroke or Working stroke): During this stroke, both the

valves will remain closed. As the combustion of fuel takes place, the burnt gases expand and

exert a large force on the piston causing it to move rapidly from the TDC to BDC.

The force (or power) is transmitted to the crankshaft through the connecting rod. As a

result, the crankshaft rotates at high speeds. The crankshaft then transmits the power through

clutches, gears, and other transmission elements to turn the wheels of the vehicle and cause it

to move. The expansion of gases is adiabatic in nature and is shown by the curve DE on p-v

diagram.

4) Exhaust stroke: During this stroke, the inlet valve remains closed and the exhaust valve

opens. The greater part of the burnt gases escape because of their own expansion. The drop in

pressure at constant volume is represented by the vertical line EB.

The piston moves from bottom dead centre to top dead centre and pushes the

remaining gases to the atmosphere. When the piston reaches the top dead centre the exhaust

valve closes and the cycle is completed.

TWO- STROKE PETROL ENGINE (2-S-P-E): In two stroke cycle engines, the suction and exhaust strokes are eliminated. There are

only two remaining strokes i.e., the compression stroke and power stroke and these are

usually called upward stroke and downward stroke. Also, instead of valves, there are inlet

and exhaust ports in two stroke cycle engines.

The burnt exhaust gases are forced out through the exhaust port by a fresh charge,

which enters the cylinder nearly at the end of the working stroke through the inlet port. The

process of removing burnt exhaust gases from the engine cylinder is known as scavenging.



1) First Stroke: At the beginning of the first stroke the piston is at the cover end .It moves

from the cover end to crank end. The spark plug ignites the compressed petrol-air mixture.

The combustion of the petrol will release the hot gases which increases the pressure in the

cylinder. The high pressure combustion gases force the piston downwards. The piston

performs the power stroke till it uncovers the exhaust port.

During the earlier part of this stroke which is performed by the pressure of the

combustion gases exerted on it, the power is produced. The combustion gases which are still

at a pressure slightly higher than the atmospheric pressure escape through the exhaust port.

As soon as the top edge of the piston uncovers the transfer port, the fresh petrol-air

mixture flows from the crankcase into the cylinder. The fresh petrol-air mixture which enters

the cylinder drives out the burnt exhaust gases through the exhaust port .This driving out of

exhaust gases by the incoming fresh charge is called scavenging. This will continue till the

piston covers both the exhaust and transfer ports during the next ascending stroke. The

crankshaft rotates by half rotation.

2) Second Stroke: In this stroke the piston moves from the crank end to cover end. When it

covers the transfer port, the supply of petrol-air mixture is cut off and then when it moves

further up it covers the exhaust port completely stops the scavenging.

Further ascend of the piston will compress the petrol-air mixture in the cylinder. The

compression ratio ranges from 1:7 to 1:11. After the piston reaches the cover end the first

stroke as explained earlier repeats again. The crankshaft rotates by half rotation.

Since this engine requires only two strokes to complete one cycle, it is called a two stroke

engine. The crankshaft makes only one revolution to complete the cycle. The power is

developed in every revolution of the crankshaft.



The two-stroke petrol engines are generally used in mopeds, scooters, motor-cycles

because they run at high speeds with moderate power outputs.

Differences between FOUR-Stroke and TWO-Stroke engine:

Sl no Principle Four-stroke engine Two-stroke engine

1 Number of strokes per cycle Four strokes per cycle Two strokes per cycle

2 Number of cycles per min Half of the speed of the

engine

n=N/2

Equal to the speed of the

engine

n=N

3 Power Power is developed in

every alternate revolution

of the crankshaft

Power is developed in

every revolution of the

crankshaft

4 Flywheel Heavy flywheel is

required

Lighter flywheel is

required

5 Admission of the charge The charge is directly

admitted into the engine

cylinder during the

suction stroke

The charge is first

admitted into the

crankcase and then

transferred to the engine

cylinder

6 Exhaust gases The exhaust gases are

driven out through the

outlet by the piston

during the exhaust stroke

The exhaust gases will be

expelled out of the

cylinder by scavenging

operation by the

incoming fresh charge

7 Valves The inlet and the exhaust

are opened and closed by

mechanical valves

The piston itself opens

and closes the inlet,

transfer and the exhaust

ports

8 Engine cooling The cooling can be made

more effective since the

combustion takes place

in alternate revolution of

the crankshaft

The rate of cooling must

be very high since the

combustion takes place

in every revolution of the

crankshaft

9 fuel consumption Fuel consumption is Less Fuel consumption is

More

10 Mechanical efficiency Less High

11 Noise Noise will be less Noise will be More

12 Uses Used in slow speed and

High power applications

like cars, trucks, tractors,

jeeps, buses etc..

Used in High speed and

Low power applications

like mopeds, scooters,

motor cycles etc..



Differences between Petrol and diesel engine (Differences between spark-ignition and

Compression-ignition engine):

Sl no Principle Petrol engine

( S I Engine)

Diesel engine

( C I Engine)

1 Working cycle Works on Otto cycle Works on diesel cycle

2 Fuel used Petrol Diesel

3 Admission of the fuel During the suction stroke

itself the petrol admitted

to the cylinder with air

At the end of the

compression stroke the

diesel is injected into the

cylinder

4 Charge drawn during the suction

stroke

Air and petrol mixture is

drawn during the suction

stroke

Only air is drawn during

the suction stroke

5 Compression ratio Low compression ratio

ranging from 7:1 to12:1

High compression ratio

ranging from 16:1 to

20:1

6 Ignition of the fuel Petrol is ignited by the

sparkplug

Diesel is ignited by

compression ignition or

self-ignition

7 Engine speed High engine speeds of

about 3000 rpm

Low engine speeds

ranging from 500 to1500

rpm

8 Power output Because of the low

compression ratio power

developed will be less

Due to high compression

ratio the power

developed will be more

9 Thermal efficiency The thermal efficiency is

less due to lower

compression ratio

The thermal efficiency is

higher due to high

compression ratio

10 Noise and vibration Because of lower

operating pressure the

noise and vibrations are

almost nil

Because of higher

operating pressure the

noise and vibrations are

high

11 Weight of the engine Weight of the engine is

less

Weight of the engine is

more

12 Initial cost Initial cost of the engine

is less

Initial cost of the engine

is more

13 Operating fuel cost Operating fuel cost is

more because petrol is

costly

Operating fuel cost is

less because diesel is

cheap

14 Maintenance cost Less Slightly higher

15 Starting of the engine The petrol engines can

easily be started even in

cold weather

The diesel engines are

difficult to start in cold

weather

16 Exhaust gas pollution The exhaust pollution is

more

The exhaust gas pollution

is less



17 Uses Used in scooter, motor

cycle, cars etc…

Used in trucks, tractors,

buses, heavy vehicles,

etc….

Advantages of a Two-Stroke engine over a Four-Stroke engine: 1) A two-stroke engine has twice the number of power strokes than a four stroke engine at

the same speed.

2) The weight of a two-stroke engine is less than the four-stroke engine because of the lighter

flywheel due to more uniform torque on the crankshaft.

3) The scavenging in more compete in two-stroke engines, since exhaust gases are not left in

the clearance volume compared to four-stroke engine.

4) Since there are no mechanical valves and valve gears, hence the construction of two-stroke

engine is simple which reduces its initial cost.

5) A two-stroke engine can be easily started compared to four-stroke engine.

6) A two-stroke engine can be easily reversed by a simple reversing gear mechanism.

7) A two-stroke engine occupies less space.

8) A two-stroke engine has less maintenance cost since it has less number of moving parts.

9) Due to light weight and high speed two-stroke engines are preferred in motor cycles,

scooters. Etc…

Disadvantages of two stroke engines: 1) Since the combustion takes place in every revolution, the time available for cooling will be

less than a four-stroke engine, which results in overheating of the piston and other engine

parts.

2) Incomplete scavenging results in mixing of the exhaust gases with the fresh charge which

will dilute it, hence lesser power output and hence low thermal efficiency.

3) Since the transfer port is kept open only for a short period, hence less quantity of charge

admitted into the cylinder which will reduce the power output.

4) Since both the transfer and exhaust ports are kept open during the same period, there is a

possibility of the escape of the fresh charge through the exhaust port which will also reduce

the thermal efficiency of the engine.

5) For a given stroke and clearance volume the effective compression stroke is less in a two-

stroke engine than in a four-stroke engine.

6) A two-stroke engine needs better cooling arrangement because of high operating

temperature.

7) The exhaust in a two-stroke engine is noisy due to the sudden release of the burnt gases.



Performance of IC Engines (ENGINE CALCULATIONS)

1. Mean effective pressure (MEP): Pm- The mean effective is defined as mean or average

pressure acting on a piston throughout the power stroke. It is also the average pressure

developed inside the engine cylinder of an IC engine. It is expressed in Bar. (1 Bar = 105

N/m2)

The mean effective pressure of an engine is obtained diagram. The indicator diagram is the p

–V diagram for one cycle at that load, drawn with the help of an indicator fitted on the

engine.

The indicated mean effective pressure is then calculated using the equation:

2. Indicated Power: Indicated power is defined as the total power developed inside the

engine cylinder due to combustion of fuel. It denoted by IP and is expressed in kW.

IP = nPmLANK/60 in watts

Where n= number of cylinders

Pm = indicated mean effective pressure in bar

L = length of stroke in m

A = cross-sectional area of the cylinder in m2

A = 𝜋𝑑2/4 where d= diameter of cylinder or bore in m

N = engine speed in rpm

K = factor used for easy simplification

K = 1/2 for four stroke engine

K = 1 for two stroke engine

When Pm is in N/m2 IP = nPmLANK/60x1000 in Kw

When Pm is in bar IP = 100nPmLANK/60 in Kw

Where 1 watt = N-m/Sec = Joule/Sec

1 bar = 105 N/m

2

3. Brake Power: The net power available at the crank shaft of the engine for performing

useful work is called brake power. It is denoted by BP and expressed in kW.



Where

N = Speed of the engine in rpm

Torque is measured by using either belt or rope brake dynamometer.

W = Net load acting on the brake drum, kg

R = Radius of the brake drum, m

T = Torque in N – m

= W * R.

4. Friction power = Indicated power – Brake power. (FP=IP-BP)KW

5. Mechanical Efficiency (ηmech): It is the efficiency of the moving parts of mechanism

transmitting the indicated power to the crankshaft. Therefore it is defined as the ratio of the

brake power and the indicated power. It is expressed in percentage.

6. Thermal Efficiency (ηThermal): it is the efficiency of the conversion of the heat energy

produced by the actual combustion of the fuel into the power output of the engine. Therefore

it is defined as the ratio of power developed by the engine by the fuel in the same interval of

time. It is expressed in percentage.

Where Heat supplied = Mf x CV

Mf = Mass of the fuel in kg

CV = Calorific value of the fuel in KJ/Kg

7. Indicated Thermal Efficiency (ɳi Thermal): Indicated thermal efficiency can be defined

as the ratio of indicated power to the heat supplied by the burning fuel.



8. Brake Thermal Efficiency (ηb Thermal): Brake thermal efficiency is defined as the ratio

of brake power to the heat supplied by the burning fuel.

9. Specific fuel consumption: SFC is defined as the amount of fuel consumed by an engine

for one unit of energy that is produced. SFC is used to express the fuel efficiency of an IC

engine .it measures the amount of fuel required to provide a given power for a given period.

It is expressed in kg/kW - hr.

Specific fuel consumption is expressed as the mass of fuel consumed per kW of power

developed per hour.

Indicated specific fuel consumption is given by

Brake specific fuel consumption is given by



MODULE – 3

MACHINE TOOLS AND AUTOMATION

MACHINE TOOLS OPERATIONS

Machine Tools and Automation: Machine Tools Operations: Turning, facing, knurling,

Thread cutting, Taper Turning by swivelling the compound rest, Drilling, Boring, Reaming,

Tapping, Counter Sinking, Counter Boring, -Plane milling, End milling, Slot milling. (No

sketches of Machine tools, sketches to be used only for explaining operations. Students to be

shown the available machine tools in the Machine Shop of the college before explaining the

operations). Robotics and Automation: Robotics: Introduction, classification based on

robots configuration; Polar, cylindrical, Cartesian Co-ordinate and spherical. Application,

Advantages, and disadvantages

Automation: Definition, types –Fixed, Programmable & Flexible automation, NC/ CNC

machines: Basic elements with simple block diagrams, advantages and disadvantages.

INTRODUCTION: Several metal cutting operations are carried out to produce a

mechanical part of required shape and size. The metal cutting operations may be carried out

either manually by using hand tools such as chisels, files, saws etc… or using metal cutting

machines. When machines perform the metal cutting operations by the cutting tools mounted

on them, they are called machine tools. A machine tool may be defined as a power driven

machine which accomplishes the cutting or machining operations on it. The fundamental

machine tools that are used for most of the machining processes are given below

1. Lathe Machine.

2. Drilling Machine.

3. Milling Machine.

4. Grinding Machine.

LATHE MACHINE: A lathe is a machine tool which turns cylindrical material, touches a

cutting tool to it, and cuts the material. It is said to be the mother of all the machine tools.

The lathe is the oldest of all machine tools and the most basic tool used in industries. A lathe

is defined as a machine tool is primarily used to produce circular objects and is used to

remove excess material by forcing a cutting tool against a rotating work piece. Lathes are

also called turning machines, since the work piece is turned or rotated between two centres.

since it is so versatile, that almost all the machining operations which are performed on other

machine tools like, drilling, grinding, shaping, milling, etc., can be performed on it.

WORKING PRINCIPLE OF LATHE:



A lathe, basically a turning machine works on the principle that a cutting tool can remove

material in the form of chips from the rotating work pieces to produce circular objects. This

is accomplished in a lathe which holds the work pieces rigidly and rotates them at high

speeds while a cutting tool is moved against it. Work piece held rigidly by one of the work

holding devices, known as chuck, and is rotated at very high speeds. A cutting tool held

against the work piece opposite to its direction of rotation when moved parallel to the axis of

the work piece produces circular surfaces as shown in figure. The material of the tool will be

harder and stronger than the material of the work piece.

LATHE OPERATIONS: All most all the basic machining operations can be performed

on a lathe. They are

1. Turning, 2. Taper turning, 3. Thread cutting, 4. Boring, 5. Facing, 6. Drilling, 7. Reaming,

8. Knurling

9. Milling, 10. Grinding

A variety of operations can be performed on a lathe. A few of them are discussed briefly

below.

Turning: - Fig shows the principle of a metal cutting operation using a single-point tool on a

lathe. The work piece is supported in between the two centres which permit the rotation of

the work piece. A single point cutting tool is fed perpendicular to the axis of the work piece

to a known pre-determined depth of cut, and is then moved parallel to the axis of the work

piece. This operation will cut the material which comes out as shown fig. This method of

machining operation in which the work piece is reduced to the cylindrical section of required

diameter is called 'Turning’.



Facing: - Facing is defined as an operation performed on the lathe to generate either flat

surfaced or shoulders at the end of the work piece. In facing operation, the direction of feed

given is perpendicular to the axis of the lathe. The work piece is held in the chuck and the

facing tool is fed either from outer edge of the work piece progressing towards the centre or

vice versa. The cutting tool is held by a tool holder in a tool post.

Knurling: - Knurling is defined as an operation performed on the lathe to generate serrated

surfaces on work pieces by using a special tool called knurling tool which impresses its

pattern on the work piece. A typical knurling tool consists of one upper roller and one lower

roller on which the desired impression pattern can be seen. The serration or impression

pattern can be straight lines or diamond pattern.



Thread Cutting :- A thread is a helical ridge formed on a cylindrical or conical rod. It is cut

on a lathe when a tool ground to the shape of the thread, is moved longitudinally with

uniform linear motion while the work piece is rotating with uniform speed as shown in Fig.

By maintaining an appropriate gear ratio between the spindle on which the work piece is

mounted, and the lead screw which enables the tool to move longitudinally at the appropriate

linear speed, the screw thread of the required pitch can be cut. The pointed tool shown in Fig,

is employed to cut V-threads. When square threads are to be cut, the tool is ground to a

squared end.

Taper turning: - Taper is defined as a uniform increase or decrease in diameter of a piece of

work measured along its length. Taper turning is an operation on a lathe to produce conical

surface on the work pieces.

Methods of Taper Turning: - 1) Taper Turning by setting over the tail Stock.

2) Taper Turning by swivelling the Compound Rest (Tool

Post).

3) Taper Turning by a Taper turning attachment.



Taper Turning by the Swivelling the Compound Tool Rest:

This method of taper turning shown in Fig. It is more suitable for work pieces, which

require steep taper for short lengths. The compound tool rest is swivelled to the required

taper angle and then locked in the angular position. The carriage is also locked at that

position. For taper turning, the compound tool rest is moved linearly at an angle so that the

cutting tool produces the tapered surface on the work piece. This method is limited to short

tapered lengths due to the limited movement of the compound tool rest.

The angle at which the compound rest to be swivelled is calculated using the equation given

below

Where

D = larger diameter of taper in mm

d = smaller diameter of taper in mm

L = length of taper in mm

α = half of taper angle in degree

DRILLING MACHINE

INTRODUCTION: Drilling is a metal cutting process carried out by a rotating cutting tool

to make circular holes in solid materials. The tool which makes the hole is called a drill. It is

generally called as twist drill, Since it has a sharp twisted edges formed around a cylindrical



tool provided with a helical groove along its length to allow the cut material to escape

through tithe sharp edges of the conical surfaces ground at the lower end of the rotating twist

drill cuts the material by peeling it circularly layer by layer when forced against a work

piece. The removed material chips get curled and escapes through the helical groove

provided in the drill. A liquid coolant is generally used while drilling to remove the heat of

friction and obtain a better finish for the hole.

DRILLING MACHINE: Drilling machine is a power operated machine tool, which holds

the drill bit in its spindle rotating at high speeds and when manually actuated to move

linearly simultaneously against the work piece produces a hole, is called drilling machine.

DRILL BIT NOMENCLATURE:

A twist drill shown in Fig.it is the cutting tool that is employed in the drilling

machines. Two long diametrically opposite helical flutes are formed throughout its effective

length. A twist drill is composed of three major parts-point, body and shank.



DRILLING MACHINE OPERATIONS: Apart from drilling, a number of other operations

that can be performed on a drilling machine using the various tools are:

1) Reaming, 2) Boring, 3) Counter boring 4) Countersinking, 5) Spot facing & 6) Tapping.

Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-

section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit

is pressed against the work piece and rotated at rates from hundreds to thousands

of revolutions per minute. This forces the cutting edge against the work piece, cutting

off chips (swarf) from the hole as it is drilled.

Reaming: - Reaming is the process of smoothing the surface of the drilled holes with a

reamer. A reamer is similar to the twist drill, but has straight flutes. After drilling the hole to

a slightly smaller size, the reamer is mounted in place of twist drill and with the speed

reduced to half of that of the drilling, reaming is done in the same way as drilling. It removes

only a small amount of material and produces a smooth finish on the drilled surfaces.

http://en.wikipedia.org/wiki/Cutting

http://en.wikipedia.org/wiki/Drill_bit

http://en.wikipedia.org/wiki/Cross_section_(geometry)

http://en.wikipedia.org/wiki/Cross_section_(geometry)

http://en.wikipedia.org/wiki/Cutting_tool

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/Revolutions_per_minute

http://en.wikipedia.org/wiki/Swarf



Boring: - Boring is done on a drilling machine to increase the size of an already drilled hole.

When a suitable size drill is not available, initially a hole is drilled to the nearest size and

using a single point cutting tool, the size of the hole is increased as shown in Fig. By

lowering the tool while it is continuously rotating, the size of the hole is increased to its

entire depth. Fig shows when the boring operation is in progress. It will be continued till the

lower surface of the work piece.

Counter boring: -Counter boring is to increase the size of a hole at one end only through a

small depth as shown in Fig. The counter boring forms a larger sized recess or a shoulder to

the existing hole. The cutting tool will have a small cylindrical projection known as pilot to

guide the tool while counter boring. The diameter of the pilot will always be equal to the

diameter of the previously drilled hole. Interchangeable pilots of different diameters are also

used for counter boring holes of different diameters. The speeds for counter boring must be

two-thirds of the drilling speed the corresponding size of the drilled hole. Generally the

counter boring is done on the holes to accommodate the socket head screws, or grooved nuts,

or round head bolts.

Countersinking: -Countersinking shown in Fig. it is the operation of making the end of a

hole into a conical shape. It is done using a countersinking tool shown in figure. The



countersinking process may also be employed for de burring the holes. The cutting speeds for

countersinking must be about one-half of that used for similar size drill. The countersunk

holes are used when the countersunk screws are to be screwed into the holes so that their top

faces have to be in flush with the top surface of the work piece.

Tapping: - The tapping, shown in Fig. it is the process of cutting internal threads with a

thread cutting tool called tap. A tap is a fluted threaded tool used for cutting internal threads.

Before tapping, a hole which is slightly smaller than the size of the tap is drilled. For cutting

the threads, the tap is fitted in the tapping attachment which in turn is mounted in the drilling

machine spindle, and the threads are cut in the same way as drilling. While tapping in a

drilling machine the spindle has to rotate at very slow speeds. The tap will be held in a

collapsible type of tapping chuck, which is inserted in the spindle of the drilling machine.

Generally tapping is done on a drilling machine when identical threading is required on large

number of parts.



INTRODUCTION

Milling: -Milling is a manufacturing process in which the excess material from the work

piece is removed by a rotating multipoint cutting tool called milling cutter.

The milling cutter is a multipoint cutting tool. The work piece is mounted on a movable work

table which will be fed against the revolving milling cutter to perform the cutting operation.

Milling machine: - A milling machine is a power operated machine tool in which the work

piece is mounted on moving table is machined to various shapes when moved under a slow

revolving serrated cutter.

PRINCIPLE OF MILLING



The above figure shows the principle of milling process that is upmilling and downmilling.

The upmilling is also called as conventional milling and downmilling is called climb milling.

The milling cutter is mounted on a rotating shaft known as arbor. The workpiece which is

mounted on the table can be fed either in the direction opposite to that of the rotating cutter

as shown in figure a or in the same direction of the cutter as shown in figure.

MILLING OPERATIONS OR PROCESSES:

The milling operations are given below

1) Plain milling , Form milling, End milling, Straddle milling, Slot milling, Gang milling,

Angular milling

Plain milling or Slab milling: -The slab milling is the operation of producing flat, horizontal

surface parallel to the axis of rotation of a slab-milling cutter. Slab milling is done to remove

the material from the upper surface of the work piece. The slab milling cutters is held in the

arbor and it may have straight or helical teethes. Both cutters can be used to generate flat

surfaces. The require depth of cut can be adjusted by raising the table or the knee and the

feed is given by moving the saddle.

End milling: -End milling is a process of milling that is used to mill slots, pockets and

keyways in such a way that the axis of the milling cutter is perpendicular to the surface of the

work piece. The milling operation when used for keyway cutting as shown in figure. The



advantage of the end milling operation is that we can achieve depth of cut of nearly of the

diameter of the mill.

Slot milling: - Slot milling is the operation of producing slots like T-slots, plain slots,

dovetail slots etc., in worktable fixtures and other work holding devices. The operation may

be performed using eighter end milling cutter, T-slot cutter, dovetail cutter or side milling

cutter. The type of cutter selected depends on the shape of the slot to be produced. Two

separate milling cutters are required for milling T-slots. Initially a side cutter or an end

milling cutter is used to cut the throat (open slot) starting from one end of the work piece to

its other end. A T-slot milling cutter is then used to cut the headspace to the desired

dimensions. Similar procedure is followed for cutting a dovetail slot, but a dovetail slot cutter

is used in place of T-slot cutter.



INTRODUCTION TO AUTOMATION

In today’s fast-moving, highly competitive industrial world, a company must be

flexible, cost effective and efficient if it wishes to survive. In the process and manufacturing

industries, this has resulted in a great demand for industrial control systems/ automation in

order to streamline operations in terms of speed, reliability and product output. Automation

plays an increasingly important role in the world economy and in daily experience.

Automation is the use of control systems and information technologies to reduce the

need for human work in the production of goods and services. In the scope of

industrialization, automation is a step beyond mechanization. Whereas mechanization

provided human operators with machinery to assist them with the muscular requirements of

work, automation greatly decreases the need for human sensory and mental requirements as

well.

Types of Automation.

Automated system can be classified into three basic types.

1. Permanent/Fixed Automation

2. Programmable Automation

3. Flexible Automation.

1. Fixed automation:-Fixed automation Fixed automation is a system in which the sequence

of processing (or assembly) operations is fixed by the equipment configuration. The

operations in the sequence are usually simple. It is the integration and coordination of many

such operations into one piece of equipment that makes the system complex.

The typical features of fixed automation are:

High initial investment for custom-engineered equipment

High production rates



Relatively inflexible in accommodating product changes.

The economic justification for fixed automation is found in products with very high demand

rates and volumes. The high initial cost of the equipment can be spread over a very large

number of units, thus making the unit cost attractive compared to alternative methods of

production.

2. Programmable automation:-In programmable automation, the production equipment is

designed with the capability to change the sequence of operations to accommodate different

product configurations. The operation sequence is controlled by a program, which is a set of

instructions coded so that the system can read and interpret them. New programs can be

prepared and entered into the equipment to produce new products. Some of the features that

characterize programmable automation include:

High investment in general-purpose equipment

Low production rates relative to fixed automation

Flexibility to deal with changes in product configuration

Most suitable for batch production

Automated production systems that are programmable are used in low and medium

volume production.

3. Flexible automation: - Flexible automation is an extension of programmable automation.

The concept of flexible automation has developed only over the last 15 to 20 years, and the

principles are still evolving. A flexible automated system is one that is capable of producing

a variety of products (or parts) with virtually no time lost for changeovers from one product

to the next. There is no production time lost while reprogramming the system and altering the

physical setup (tooling, fixtures and machine settings). Consequently, the system can produce

various combinations and schedules of products, instead of requiring that they be made in

separate batches.

The features of flexible automation can be summarized as follows:

High investment for a custom-engineered system

Continuous production of variable mixtures of products

Medium production rates

Flexibility to deal with product design variations

High unit cost

Advantages and disadvantages of Automation:

The main advantages of automation are:

Replacing human operators in tasks that involve hard physical work.

Replacing humans in tasks done in dangerous environments (i.e. fire, space,

volcanoes, nuclear facilities, underwater, etc.)



Performing tasks that are beyond human capabilities of size, weight, speed,

endurance,etc.

Safer working conditions.

Automation results in reduces total cost per unit output.

Better product quality and consistent in accuracy.

The main disadvantages of automation are:

High initial cost for equipment’s and technologies.

High maintenance costs.

Increase in un-employment.

Not suitable for short product life cycle.

Not economically justifiable for small scale production.

INTRODUCTION TO NC MACHINES:

Numerical control can be defined as a form of programmable automation in which process is

controlled by numbers, letters and symbols. In NC, the numbers form a programme of

instructions designed for a particular work part or job. When job changes the program of

instruction changes. This capability to change a program for each new job gives NC its

flexibility.

Basic components of NC system:

An operational numerical control system consists of the following three basic components:

1. Program of instructions.

2. Controller unit also called machine tool unit (MCU),

3. Machine tool or other controlled process.

The program of instructions serves as input to the controller unit, which in turn commands

the machine tool or other process to be controlled.

Program of Instructions:-The program of instructions is the detailed step by step set of

instructions which tell the machine what to do. It is coded in numerical or symbolic form on



some type of input medium that can be interpreted by the controller unit. The most common

one is the 1-inch-wide punched tape. Over the years, other forms of input media have been

used, including punched cards, magnetic tape, and even 35mm motion picture film. There are

two other methods of input to the NC system which should be mentioned. The first is by

manual entry of instructional data to the controller unit. This is time consuming and is rarely

used except as an auxiliary means of control or when one or a very limited no. of parts to be

made. The second method of input is by means of a direct link with the computer. This is

called direct numerical control, or DNC.

Controller Unit: - The second basic component of NC system is the controller unit. This

consists of electronics and hardware that read and interpret the program of instructions and

convert it to mechanical actions of the machine tool. The typical elements of the controller

unit include the tape reader, a data buffer, signal output channels to the machine tool, and the

sequence controls to coordinate the overall operation of the foregoing elements.

The tape reader is an electrical-mechanical device for the winding and reading the

punched tape containing the program of instructions. The signal output channels are

connected to the servomotors and other controls in machine tools. Most N.C. tools today are

provided with positive feedback controls for this purpose and are referred as closed loop

systems. However there has been growth in the open loop systems which do not make use of

feedback signals to the controller unit. The advocates of the open loop concept claim that the

reliability of the system is great enough that the feedback controls are not needed.

Machine Tool: - The third basic component of an NC system is the machine tool or other

controlled process. It is part of the NC system which performs useful work. In the most

common example of an NC system, one designed to perform machining operations, the

machine tool consists of the worktable and spindle as well as the motors and controls

necessary to drive them. It also includes the cutting tools, work fixtures and other auxiliary

equipment needed in machining operation.

Advantages and disadvantages of NC MACHINES:

The following few are advantages and disadvantages of NC machines.

Advantages:

1. Higher productivity.

2. Higher precision with better quality control of products.

3. Multi operational facilities (or tasks).

4. Does not require a skilled operator.

Disadvantages:

1. High initial cost of equipment’s,

2. Maintenance cost.

3. Required skilled personal to execute a program.



4. Tapes tend to wear and become dirty on frequent use and thus may become

unreadable.

5. Punched tape needs to be recycled for each product of that batch.

INTRODUCTION TO NC MACHINES:

Computer Numerical Control (CNC) is defined as an NC system who’s MCU is

based on a dedicated Microcomputer rather than on a hard-wired controller. The latest

computer controllers for CNC feature high speed processors, large memories, solid-state

flash memory, improved servos, and bus architectures. Some controllers have the capability

to control multiple machines.

FEATURES OF CNC:

Computer NC system include additional features beyond what is feasible with conventional

hard-wired NC.

The features, many of which are standard on most CNC MCUs, include the following.

1. Storage of more than one part program. With improvements in computer storage

technology, newer CNC controllers have sufficient capacity to store multiple programs.

2. Various forms of program input. Whereas conventional (hard-wired) MCUs are limited to

punched tape as the input medium for entering part programs, CNC controllers generally

process multiple data entry capabilities, such as punched tape (if the machine stop still uses

punched tape), magnetic tape, floppy diskettes, RS-232 communications with external

computers, and manual data input (operator entry of program).

3. Program editing at the machine tool. CNC permits a part program to be edited while it

resides in the MCU computer memory. Hence, a program can be tested and corrected entirely

at the machine site, rather than being returned to the programming office for corrections.

4. Diagnostics. Many modern CNC systems possess a diagnostics capability that monitors

certain aspects of the machine tool to detect malfunctions or signs of impeding malfunctions

or to diagnose system breakdowns.

5. Communication interface. With trend toward interfacing and networking in plants today,

most modern CNC controllers are equipped with a standard RS-232 or other communications

interface to link the machine to other computers and computer driven devices.



THE MACHINE CONTROL UNIT FOR CNC

The MCU is the hardware that distinguishes CNC from conventional NC. The general

configuration of the MCU in a CNC system is illustrated in Figure 8. The MCU consists of

following components and sub systems: (1) central processing unit, (2) memory (3) I/O

interface, (4) controls for machine tool axes and spindle speed, and (5) sequence controls for

other machine tool functions.

Central processing unit. The central processing unit (CPU) is the brain of the MCU. It

manages the other components in the MCU based on software contained in main memory.

The CPU can be divided into three sections: (1) control section, (2) arithmetic-logic unit, and

(3) intermediate access memory.

Memory. The immediate access memory in the CPU is not intended for storing CNC

software. A much greater storage capacity is required for the various programs and data

needed to operate the CNC system.

Input/output interface. The I/O interface provides communication between the various

components of the CNC system, other computer systems, and the machine operator. As its

name suggests, the I/O interface transmits and receives data and signals to and from external

devices.

Controls for machine tool axes and spindle speed. These are hardware components that

control the position and velocity (feed rate) of each machine axis as well as the rotational

speed of the machine tool spindle.

Sequence controls for other machine tool functions. In addition to control of table

position, feed rate, and spindle speed, several additional functions are accomplished under

part program control. These auxiliary functions are generally on/off actuations, interlocks,



and discrete numerical data. To avoid overloading of CPU, a programmable logic controller

is sometimes used to manage the I/O interface for these auxiliary functions.

Advantages of CNC Machine:

• It eliminates human errors.

• Higher flexibility.

• High accuracy.

• Wastage is minimum.

• Suitable for batch production less space is required.

• Reduces inspection cost.

• More operational safety.

• Quality of product is high.

Disadvantages of CNC Machine

• Initial cost is high.

• It requires skilled programmers.

• It is not suitable for small scale production.

• Maintenance cost is more.

Major difference between NC and CNC machines as fallows.

NC Machine CNC Machine

The punched tape is

cycled

through the reader for every work piece in

the batch

The program is entered once and

then stored in computer memory

It has no additional flexibility and

computational capability

It has additional flexibility

and

computational capability

The hardware NC controller unit is present The conventional hardware NC control

unit is replaced by microcomputer

We cannot easily refine. change and

improve the part programming procedure

Use of computers refines, change and

improves part programming procedure

through interactive graphic techniques

Total factory automation with the help of

NC machines not easily possible

Total factory automation is easily

possible and is more compatible

Adaptive control and in-process

compensation cannot be done with the

help of NC machine

Use of adaptive control and in-process

compensation optimize the working

conditions



The system is rigid System is flexible

Data are stored in the tape to the control

unit Data may be stored or directly sent

Modifications are not easy Modifications can be done very easily

ROBOTICS:

Introduction: An industrial robot is a general – purpose, programmable machine processing

certain

Anthropomorphic characteristics. The most obvious anthropomorphic characteristic of an

industrial robot is its mechanical arm, which is used to perform various industrial tasks.

Other human – like

Characteristics are the robot’s capabilities to respond to sensory inputs, communicate with

other machines, and make decisions. These capabilities permit robot to perform a variety of

useful tasks. The development of robot technology followed the development of numerical

control, and the two technologies are quite similar. They both involve coordinate control of

multiple axes (the axes are called joints in robot), and they both use dedicated digital

computers as controllers. The robots are designed for a wider variety of tasks. Typical

production applications of industrial robots include spot welding, material transfer, machine

loading, spray painting, and assembly.

Some of the qualities that make the industrial robots commercially and technologically

important are

Listed here.

Robots can be substituted for humans in hazardous or uncomfortable work

environments.

A robot performs its work cycle with a consistency and repeatability that cannot be

attained by humans.

Robots can be programmed. When the production run of the current task is

completed, a robot can be reprogrammed and equipped with the necessary tooling to

perform an altogether different task.

Robots are controlled by computers and can therefore be connected to the computer

systems to achieve computer integrated manufacturing.

ROBOT ANATOMY AND RELATED ATTRIBUTES

The manipulator of an industrial robot consists of a series of joints and links. Robot anatomy

is concerned with the type and size of these joints and links and other aspects of the

manipulator’s physical construction.

Joints and links



A joint of an industrial robot is similar to a joint in human body; it provides relative motion

between two parts of the body. Each joint, or axis as it is sometimes called, provides the

robot so-called degree-of freedom (DOF) of motion. In nearly all cases, only one degree-of-

freedom is associated with each joint. Robots are often classified according to the total

number of degree-of-freedom they possess. Connected to each joint are two links, an input

link and output link. Links are the rigid components of the robot manipulator. The purpose of

the joint is to provide controlled relative movement between the input link and the output

link.

Most robots are mounted on a stationery base on the floor. Let us refer to this base and its

connection to the first joint as link 0. It is the input link to joint1, the first in the series of joint

used in the construction of the robot. The output link of the joint 1 is link 1. Link 1 is the

input link to joint 2, whose output link is link 2, and so forth. This joint-link numbering

scheme is illustrated in figure below.

Diagram of robot construction showing how a robot is made up of a series of joint-link

combination

Nearly all industrial robots have mechanical joints that can be classified into one of five

types; two types that provide translation motion and three types that provide rotary motion.

These joint types are illustrated in Fig’s the five joint types are

1. Linear joint (type L joint). The relative movement between the input link and the

output link is a Translational sliding motion, with the axes of the two links parallel.



2. Orthogonal joint (type O joint). This is also a translation sliding motion, but the input

and output links are perpendicular to each other during move.

3. Rotational joint (type R joint). This type provides rotational relative motion, with the

axis of rotation perpendicular to the axes of the input and output link.

4. Twisting joint (type T joint). This joint also involves rotary motion, but the axis of

rotation is parallel to the axes of the two links.

Each of these joint types has a range over which it can be moved. The range for a

translational joint is



Usually less than a meter, but for large gantry robots, the range may be several meters. The

three types of rotary joints may have a range as small as few degrees of as large as several

complete turns.

Classification based on ROBOT configurations:

Industrial robots are designed to have various arm manipulations so as to have motion in

different directions. The possible types of arm movements that a robot is designed with

defines configurations.

A robot can have any one the following configurations.

• Cartesian configuration

• Cylindrical configuration

• Polar configuration

• Jointed – arm configuration

• SCARA(selective compliance assembly robot arm)

1. CARTESIAN CONFIGURATION ROBOT:

Cartesian configurations robot is so called because the Arm movement of robot is designed to

move parallel to x, y, z-axis of a Cartesian coordinate system as show in figure. A robot

designed with this type of configurations Capable of moving its arm to any point linearly

within rectangular work space. Since the arm movement in linear, the robot is also called as

rectilinear or gantry robot.

Advantages:

Simple control due to linear movement and also easy visualize.

High degree of mechanical rigidity, accuracy and repeatability.

It able to carry heavy loads.

Movement can start and stop simultaneously along all three axis, motion of wrist end

is smoother.



Disadvantages:

The arm movement is limited to a small rectangular work space.

Occupy large space.

Low ratio of robot size to operate volume

Applications: Assembly, welding, machine loading and unloading, surface finishing,

inspection, etc.

2. CYLINDRICAL CONFIGURATION ROBOT:

The cylindrical configuration combines both vertical (z-axis) and horizontal (x-axis)

linear movements with rotary movement in the horizontal plane about vertical axis (y-axis).

It is also called so because its motions sweep out a partially cylindrical working volume.

This robot configuration finds application in radial workplace layout where the work

approached primarily in the horizontal plane and where no obstructions are present.

A typical cylindrical configuration is illustrated in fig. It consists of a base, a

horizontal arm and a prismatic joint built into the horizontal around the vertical column,

describing a partial cylinder in space. The prismatic joint can slide in and out remaining

parallel to the base.



Advantages:

Larger work space than Cartesian configuration.

Robot is relatively easy to program.

Applications: machine loading and unloading, investment casting, forging operations,

conveyor pellet transfer, assembly, coating applications etc.

3. POLAR CONFIGURATION OR SPHERICAL CONFIGURATION:

The geometry of the spherical or polar configuration combines rotational movement

in both horizontal and vertical planes with a single linear movement of the arm.

This configuration occupies and sweeps out a relatively large volume and access of

the arm within this total volume is restricted.

This robot rotates about the vertical axis (T joint) of its waist on the base. The second

axis is a horizontal rotary joint (R joint) allowing arm to rotate in a vertical plane. Making

use of both axes, the arm can sweep through a partial sphere of radii depending on the length

of the prismatic joint (L joint) shown in fig

Advantages:

Configuration is simple in design, and hence easy to program.

Provides good weight lifting capabilities.



Applications: Die-casting, injection moulding, forging, machine tool press, material transfer

applications.

4. JOINTED – ARM CONFIGURATION ROBOT:

This robot manipulator has the general configuration of human arm. Consisting two

straight component’s corresponding to the human forearm and upper are mounted on a

vertical pedestal that can be rotated about the base. The jointed arm configuration shown in

fig. consists of a vertical column that swivels about the base using a T joint.

At the top of the column is a shoulder joint (R joint), whose output link connects to an

elbow joint (R joint).

Advantages of robots

Robotics and automation can, in many situation, increase productivity, safety,

efficiency, quality and consistency of product.

Robots can work in hazardous environments.

Robots need no environmental comfort.

Robots work continuously without any humanity needs and illness.

Robots have repeatable precision at all times.

Robots can be much more accurate than humans; they may have milli or micro inch

accuracy.



Robots and their sensors can have capabilities beyond that of humans.

Robots can process multiple tasks simultaneously but humans can only one.

Robots replace human workers who can create economic problem.

Disadvantages of robots

Robots lack capability to respond in emergencies, this can cause.

o In appropriate and wrong response

o A lack of decision making power

o A loss of power

o Damage to the robot and other devices

o Human injuries

Robots may have limited capabilities in

Degrees of freedom

Dexterity

Sensors

Vision system.

Real – time response

Robots are costly due to

Initial cost of equipment

Installation cost

Need for peripherals

Need for training

Need for programming.

Robot applications

• Need to replace human labor by robot.

• Work environment hazardous for human beings.

• Repetitive task

• Boring and unpleasant task

• Multi shift operations

• Operating for long hours without rest

• Assembly applications

• Material handling applications

• Processing operations

• Inspection applications

.



MODULE – 4

ENGINEERING MATERIALS AND JOINING

PROCESSES

Engineering materials and joining processes: Engineering Materials: Types and

applications of Ferrous & Nonferrous metals and alloys, Composites: Introduction:

Definition, Classification and applications (Air craft and Automobiles) Soldering, Brazing

and Welding: Definitions, classification and method of soldering, Brazing and welding.

Differences between soldering, brazing and Welding. Description of Electric Arc Welding

and Oxy-Acetylene Welding.

Introduction: materials are various kinds are developed and it is difficult to describe all of

them in a single text. Here, it is confined to study of those materials which are commonly

used for various engineering applications. These materials have also a set of properties which

are used for specific applications. Selections of materials for specific project/applications is

an important activity for success and failure of that project.

Metals :-A metals a material that is typically hard, opaque, shiny, and features good

electrical and thermal conductivity. Metals are generally malleable: they can be hammered or

pressed permanently out of shape without breaking or cracking well as fusible and ductile

Metals can be either ferrous or non-ferrous. Ferrous metals contain iron while non-ferrous

metals do not both ferrous and non-ferrous metals are divided into pure metals and alloys.

A pure metal is an element – Ex: iron, copper, gold- unalloyed (not mixed) with another

substance.

An alloy is a mixture of two or more elements (Ex: iron and carbon) to make

another metal with particular properties (Ex: steel).

Classification and Selection of Materials:

The first module deals with the classification of the engineering materials and their

processing techniques. The engineering materials can broadly be classified as:

a) Ferrous Metals

b) Non-ferrous Metals (aluminium, magnesium, copper, nickel, titanium)

c) Plastics (thermoplastics, thermosets)

d) Ceramics and Diamond

e) Composite Materials

f) Nano-materials.



Ferrous metals: - Ferrous metals contain iron. Examples are cast iron, mild steel, medium

carbon steel, high carbon steel, stainless steel, and high speed steel.

Atomic number of iron is 26. Fe.

Non-ferrous metals: - Non-ferrous metals do not contain iron. Some common on-ferrous

metals are aluminium, copper, zinc, tin, brass (copper + zinc), and bronze (copper + tin).

Type of Ferrous metal

Pig iron :- is the intermediate product of smelting iron ore with a high-carbon fuel such

as coke, usually with limestone as a flux. It is the molten iron from the blast furnace, which is

a large and cylinder-shaped furnace charged with iron ore, coke, and limestone. Charcoal and

anthracite have also been used as fuel. Pig iron has a very high carbon content, typically 3.5–

4.5%, along with silica and other constituents of dross, which makes it very brittle and not

useful directly as a material except for limited applications.

Wrought iron: - is an iron alloy with a very low carbon (less than 0.08%) content in contrast

to cast iron (2.1% to 4%), and has fibrous inclusions known as slag up to 2% by weight. It is

a semi-fused mass of iron with slag inclusions which gives it a "grain" resembling wood that

is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable,

ductile, corrosion-resistant and easily welded. Before the development of effective methods

of steelmaking and the availability of large quantities of steel, wrought iron was the most

common form of malleable iron.

Cast iron;- Composition Alloy of iron and 2-5% carbon, 1-3% silicon and traces of

magnesium, sulphur and phosphorus

Cast iron is iron or a ferrous alloy which has been heated until it liquefies, and is then poured

into a mould to solidify. It is usually made from pig iron. The alloy constituents affect its

colour when fractured: white cast iron has carbide impurities which allow cracks to pass

straight through. Grey cast iron has graphite flakes which deflect a passing crack and initiate

countless new cracks as the material breaks. Carbon (C) and silicon (Si) are the main alloying

elements, with the amount ranging from 2.1–4 wt. % and 1–3 wt. %, respectively. Iron alloys

with less carbon content are known as steel. While this technically makes these base alloys

ternary Fe–C–Si alloys, the principle of cast iron solidification is understood from

the binary iron–carbon phase diagram. Since the compositions of most cast irons are around

the eutectic point of the iron–carbon system, the melting temperatures closely correlate,

usually ranging from 1,150 to 1,200 °C (2,100 to 2,190 °F), which is about 300 °C (572 °F)

lower than the melting point of pure iron.

Properties and characteristics: -Hard skin, softer underneath, but brittle. It corrodes by

rusting.

Application: -Parts with complex shapes which can be made by casting

http://en.wikipedia.org/wiki/Intermediate_product

http://en.wikipedia.org/wiki/Smelting

http://en.wikipedia.org/wiki/Iron_ore

http://en.wikipedia.org/wiki/Coke_(fuel)

http://en.wikipedia.org/wiki/Limestone

http://en.wikipedia.org/wiki/Flux_(metallurgy)

http://en.wikipedia.org/wiki/Blast_furnace

http://en.wikipedia.org/wiki/Charcoal

http://en.wikipedia.org/wiki/Anthracite

http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Dross

http://en.wikipedia.org/wiki/Brittle

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Alloy


http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Slag

http://en.wikipedia.org/wiki/Steelmaking


http://en.wikipedia.org/wiki/Ferrous


http://en.wikipedia.org/wiki/Pig_iron

http://en.wikipedia.org/wiki/Carbide

http://en.wikipedia.org/wiki/Grey_iron


http://en.wikipedia.org/wiki/Silicon

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Binary_compound

http://en.wikipedia.org/wiki/Eutectic_point



Gray iron, or grey cast iron:-is a type of cast iron that has a graphitic microstructure. It is

named after the gray colour of the fracture it forms, which is due to the presence of graphite.

It is the most common cast iron and the most widely used cast material based on weight.

Application:-automotive engine blocks, gears, flywheels, frames.

White cast iron displays white fractured surface due to the presence of cementite. With a

lower silicon content (graphitizing agent) and faster cooling rate, the carbon in white cast

iron precipitates out of the melt as the metastable phase cementite, Fe3C, rather than graphite.

Composition:-1.8 to 3.6%carbon, 0.5to2.0%silicon. Along with sulphur.

Application: - car wheels, sprockets, rolling mills rolls.

Malleable iron starts as a white iron casting that is then heat treated at about 900 °C

(1,650 °F). Graphite separates out much more slowly in this case, so that tension has time to

form it into spheroidal particles rather than flakes.

Composition: -2.0 to 3.0%carbon, 0.6 to 1.3%silicon. Along with sulphur.

Applications: - universal joints, yokes, differential gears, compressors, crankshaft and

flanges.

Mild steel: - Composition: -Alloy of iron and 0.15 - 0.3% carbon, Properties and

characteristics: -Tough, ductile and malleable. Good tensile strength, poor resistance to

corrosion

Application: -General-purpose engineering material.

Steels: - are alloys of iron and carbon, widely used in construction and other applications

because of their high tensile strengths and low costs. Carbon, other elements, and inclusions

within iron act as hardening agents that prevent the movement of dislocations that otherwise

occur in the crystal lattices of iron atoms.

The carbon in typical steel alloys may contribute up to 2.1% of its weight. Varying the

amount of alloying elements, their formation in the steel either as solute elements, or as

precipitated phases, retards the movement of those dislocations that make iron so ductile and

weak, or thus controls qualities such as the hardness, ductility, and tensile strength of the

resulting steel. Steel's strength compared to pure iron is only possible at the expense

of ductility, of which iron has an excess.

Low carbon steel: - 0.05-0.1% carbon content.

Application: -valves, small gears, screws, rivets, nuts, pins etc...

Medium carbon steel; - Composition: -Alloy of iron and 0.35 - 0.7% carbon

Properties and characteristics: -Strong, hard and tough, with a high tensile strength, but less

ductile than mild steel.

http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Graphite

http://en.wikipedia.org/wiki/Fracture

http://en.wikipedia.org/wiki/Metastable

http://en.wikipedia.org/wiki/Cementite

http://en.wikipedia.org/wiki/Heat_treatment




http://en.wikipedia.org/wiki/Tensile_strength

http://en.wikipedia.org/wiki/Dislocation

http://en.wikipedia.org/wiki/Crystal_lattice

http://en.wikipedia.org/wiki/Hardness_(materials_science)

http://en.wikipedia.org/wiki/Ductility

http://en.wikipedia.org/wiki/Ductile



Application: -springs; any application where resistance to wear is needed

High carbon steel; - Composition: -Alloy of iron and carbon: 0.7 - 1.5% carbon

Properties and characteristics: -Even harder than medium carbon steel, and more brittle. Can

be heat-treated to make it harder and tougher

Application: -Cutting tools, mechanical elements

Stainless steel:-Composition: -Alloy of iron and carbon with 16-26% chromium, 8-22%

nickel and 8% magnesium

Properties and characteristics: -Hard and tough, resists wear and corrosion

Application: -Cutlery, kitchen equipment

High speed steel:-Composition: -Alloy of iron and 0.35 - 0.7% carbon (medium carbon

steel) with tungsten, chromium, vanadium, and sometimes cobalt

Properties and characteristics: -Very hard, high abrasion- and heat resistance

Application: -Cutting tools for machines

Type of Non Ferrous metal

Aluminium: - Aluminium (or aluminium; see spelling differences) is a chemical element in

the boron group with symbol Al and atomic number 13. It is a silvery white, soft,

nonmagnetic, ductile metal. Aluminium is the third most abundant element (after oxygen and

silicon), and the most abundant metal in the Earth's crust. It makes up about 8% by weight of

the Earth's solid surface.

Composition: -Pure aluminium (an element)

Properties and characteristics: -Good strength-to-weight ratio, light, soft, ductile, good

conductor of heat and electricity

Application Kitchen equipment, window frames, general cast components

Copper: - Copper is a chemical element with symbol Cu (from Latin: cuprum) and atomic

number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure

copper is soft and malleable; a freshly exposed surface has a reddish-orange colour. It is used

as a conductor of heat and electricity, a building material, and a constituent of various

metal alloys.

Composition: -Pure copper (an element), Properties and characteristics: -Malleable and

ductile, good conductor of heat and electricity, resistant to corrosion

Application Water pipes, electrical wire, decorative goods

Zinc: - Zinc, in commerce also spelter, is a chemical element with symbol Zn and atomic

number 30. It is the first element of group 12 of the periodic table. In some respects zinc is

http://en.wikipedia.org/wiki/Aluminium#Etymology

http://en.wikipedia.org/wiki/Chemical_element

http://en.wikipedia.org/wiki/Boron_group

http://en.wikipedia.org/wiki/Atomic_number


http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Element_abundance

http://en.wikipedia.org/wiki/Earth

http://en.wikipedia.org/wiki/Crust_(geology)


http://en.wikipedia.org/wiki/Latin_language




http://en.wikipedia.org/wiki/Electrical_conductivity


http://en.wikipedia.org/wiki/Spelter


http://en.wikipedia.org/wiki/Group_12_element

http://en.wikipedia.org/wiki/Periodic_table



chemically similar to magnesium: its ion is of similar size and its only common oxidation

state is +2. Zinc is the 24th most abundant element in Earth's crust and has five

stable isotopes.

Composition: -Pure zinc (an element), Properties and characteristics: -Weak metal,

extremely resistant to corrosion

Application; - Usually used for coating steel to make galvanised items

Brass: - Brass is an alloy made of copper and zinc; the proportions of zinc and copper can be

varied to create a range of brasses with varying properties. It is a substitution: atoms of the

two constituents may replace each other within the same crystal structure.

Composition: -Alloy of copper and zinc, Properties and characteristics: - Resistant to

corrosion, fairly hard, good conductor of heat and electricity

Application; - Cast items such as water taps, ornaments

Bronze:- Bronze is an alloy consisting primarily of copper and the addition of other metals

(usually tin) and sometimes arsenic, phosphorus, aluminium, manganese, and silicon. These

additions produces an alloy much harder than copper alone. The historical period where the

archaeological record contains many bronze artifacts is known as the Bronze Age.

Composition: -Alloy of copper and tin, Properties and characteristics: -Fairly strong,

malleable and ductile when soft

Application; - Decorative goods, architectural fittings

Tin: - Tin is a chemical element with the symbol Sn (for Latin: stannum) and atomic

number 50. It is a main group metal in group 14 of the periodic table. Tin shows a chemical

similarity to both neighbouring group-14 elements, germanium and lead, and has two

possible oxidation states, +2 and the slightly more stable +4.

Composition: -Pure tin (an element), Properties and characteristics: -Soft, weak, malleable,

ductile and resistant to corrosion

Application; - Usually used for coating steel to form tinplate

Composites

Definition of Composite Materials

A composite is combination of two materials in on a Macroscopic level and are not

soluble in each other in which one of the materials, called the reinforcing phase, is in the

form of Fibres, sheets, or particles, and is embedded in the other materials called the matrix

phase.

The reinforcing material and the matrix material can be metal, ceramic, or

polymer. Composites typically have a Fibre or particle phase that is stiffer and stronger

http://en.wikipedia.org/wiki/Magnesium

http://en.wikipedia.org/wiki/Ion

http://en.wikipedia.org/wiki/Oxidation_state


http://en.wikipedia.org/wiki/Isotope


http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Zinc


http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Tin

http://en.wikipedia.org/wiki/Arsenic

http://en.wikipedia.org/wiki/Manganese

http://en.wikipedia.org/wiki/Silicon

http://en.wikipedia.org/wiki/Bronze_Age


http://en.wikipedia.org/wiki/Latin_language



http://en.wikipedia.org/wiki/Main_group_element

http://en.wikipedia.org/wiki/Group_14

http://en.wikipedia.org/wiki/Periodic_table

http://en.wikipedia.org/wiki/Germanium

http://en.wikipedia.org/wiki/Lead




than the continuous matrix phase and serve as the principal load carrying members. The

matrix acts as a load transfer medium between Fibres, and in less ideal cases where

the loads are complex, the matrix may even have to bear loads transverse to the

Fibre axis. The matrix also serves to protect the Fibres from environmental damage

before, during and after composite processing. When designed properly, the new

combined material exhibits better strength than would each individual material.

Composites are used not only for their structural properties, but also for electrical, thermal,

tribological and environmental applications

Classification of composite material

I. Polymer composite: - It consists of polymer resin as the matrix material. The term resin

is used in this context to denote a high molecular weight re-enforcing plastic. These

material are used as matrix material in great diversity of composite application, as well

as in large quantities because of their excellent room temp properties, ease of fabrication,

highly economical costs. Thermoplastic polymer and thermosetting polymers are used

extensively as matrix material.

Thermoplastic are soften when heated and hardened when cooled. Processes are totally

reversible. Thermosetting are become permanently hard when heated and do not soften

upon subsequent heating.

II. Ceramics composite:- Ceramics materials are very well known for their high temp

properties as well as their resistance to oxidation. But they are very brittle which limits

their application. Ceramics which are commonly used as matrix material are silicon

nitride, silicon carbide, alumina, zirconium dioxide but it is fact that ceramics make better

reinforcement material than matrix material.

III. Metal- matrix composite: - Metal matrixes composite are those where metal or alloys

are used as matrix material. Metals used are usually ductile in nature and reinforced with

strong and low density material of all shapes-fibres, whiskers and particulate. Such

combination helps in obtaining materials with improved stiffness, abrasion resistance, creep

resistance, thermal conductivity and dimensional stability. Some of the advantages of



metal matrix composite over polymer-matrix composite include higher operating

temperature, non-flammability and greater resistance to degradation by original fluids.

But MMC’s are more expensive.

Ia). Fibre reinforced composite:- Fibre reinforced composite are those where

the reinforcement in form of fibre. A natural example for fibre reinforce composite is

wood in which strong cellulose fibre are aligned in a base matrix of lignin which bind the

fibres. A Fibre is characterized by its length being much greater compared to its cross-

sectional dimensions. The dimensions of the reinforcement determine its capability of

contributing its properties to the composite.

Technologically the most important type of composites is fibre reinforced ones

because of their wide range of application. The characteristics of fibre reinforced composite

are expressed in terms of specific strength and specific modulus parameters. Specific strength

is nothing but the ratio of tensile strength to specific gravity whereas specific modulus is

the ratio of young’s modulus to specific gravity. Fibre reinforced composites with

exceptionally high specific strength and moduli have been successfully produced using

fibres of different material.

ii. Laminated composites:-fibre –reinforced composites, if the fibres are of uniform

alignment, the composites show anisotropic properties i.e., different properties along

different direction. But if layers of such composites are stacked and bonded together in such

a way that successive layers have their fibres aligned in different direction, the composite on

the whole will have high strength and uniform properties in all direction.



The best example for a laminated for laminated composites is plywood where successive

layers of wood having different orientation of grains are cemented together and

composite on the whole has better strength in all direction.

iii. Particulate composites In particulate composites the reinforcement is of particle

nature. It may be spherical, cubic, tetragonal, a platelet, or of other regular or irregular

shape. In this type of composites, particles of varying shape and size of one material is

dispersed in a matrix of second material. Particulate composites are similar in

construction to dispersion strengthened alloys but differ in particle size and percentage by

volume.



Application of composite material

Fibre reinforced composites

I. Fibre glass which is a composite consisting of glass fibres within a polymer matrix is

extensively used to make pipe, roofing’s, storage container, industrial floorings,

automotive and marine bodies.

II. Carbon reinforced polymer composites are widely utilized in making sports and

recreational equipment, pressure vessels, aircraft structural components.

III. Boron fibre reinforced polymer composite have been used in military air craft

components, helicopter rotor blades and some sporting goods

IV. Silicon carbides and alumina fibre reinforced composites are utilized in tennis

rackets, circuit boards and nose cone.

V. Filament winded fibre reinforced plastics which have extremely high tensile strengths

are used to make chemical and fuel storage tanks, pressure vessels.

VI. Hybrid composite which is obtained by using two or more different kind of

fibres in a single matrix. They have a better all-around combination of properties

than composites containing only a single fibre type. A polymer composite

reinforced with both carbon and glass fibre is used in sporting goods and light

weight orthopaedic component.

Ceramics composites

A. Concrete which contains steel rods in a matrix of cement, sand and crushed stones is

extensively used in construction.

B. Silicon carbide particles reinforced in titanium-di-boride matrix has good wear and

corrosion resistance and hence can be used to produce heat exchangers.

Metal-Matrix composites

1) Boron fibre reinforced aluminium alloy matrix composite is used as a material

to make some structural members in space shuttles owing to its very high strength to

weight ratio.

2) Particulate alumina reinforced in aluminium matrix finds application in

producing sporting equipment automobile engine parts.

SOLDERING, BRAZING AND WELDING

Soldering: - Soldering is a method of uniting two thin metal pieces using a dissimilar metal

or alloy by the application of heat. The alloy of lead and tin is called soft solder, is used in

varying proposition for sheet metal work, plumbing work and electrical junctions. The



melting temp of the soft solder will be between 150 to 50 C. To clean the joint surfaces

and to prevent oxidation a suitable flux is used while soldering. Zinc chloride is the

flux that is commonly used in soft soldering. A soldering iron is used to apply the heat

produced from the electrical source. An alloy of copper, tin, and silver known as hard solder

is used for stronger joint. The soldering temp of hard solder ranges from 00 to 00 C

Method of soldering

a. Cleaning of joining surfaces

b. Application of flux

c. Tinning of surface to be soldered

d. Heating

e. Final clean-up

(i) Cleaning of joining surfaces: Firstly, the joining surface are cleaned mechanically to

make free from dust, oil scale, etc. and ensure that the molten filler metal wets the surfaces.

(ii) Application of flux: Then the joining surfaces are coated with a flux usually rosin or

borax. This cleans the surfaces chemically and helps the soldering making bond.

(iii) Tinning of surface to be soldered: before carrying out the soldering operation, the

soldering iron must be tinned. This is to remove a thin film of oxide that forms on the copper

bit, which in turns does not allow the job to be heated and thus it becomes difficult to solder.

In tinning the copper bit is heated and then rubbed with a file to clean it properly and

then rotating with solder using resin. This causes the formation of a thin film of solder

over the copper bit. This whole process is called tinning

(iv) Heating: the soldering iron is then heated and flowing molten filler metals fills the joints

interface. Allow the soldered area to cool and then solidify thus making the joint.

(v) Final clean-up: after completing the soldering and joints are formed, clean it with

steel wool or solvent to remove left over flux. After this clean the soldering iron using a

damp sponge.

Advantages of soldering

1. Low cost and easy to use

2. Soldered joints are easy to repair or do rework

3. The soldered joint can last for many year

4. Low energy is required to solder

5. An experienced person can exercise a high degree of control over the soldering process



Disadvantages of soldering

1. Not suitable for heavy sections

2. Temperature is limited

3. Strength is limited.

Brazing:- Brazing is the method of joining two similar or dissimilar metals using a

special fusible alloy. Joints formed by brazing are stronger than that of soldering. During

the brazing, the base metal of the two pieces to be joined is not melted. The filler metal must

have ability to wet the surfaces of the base metal to which it is applied. Some diffusion or

alloying of the filler metal with base metal takes place even though the base metal

does not reach its melting temp. The materials used in brazing are copper base and silver

base alloy. These two can be classified under the name spelter.

Method of brazing

1. Cleaning the surface of the parts.

2. Application of flux at the place of joint.

3. Common borax and mixture of borax and boric acid is used as flux.

4. The joint and the filler material are heated by gas welding torch above the melting

temperature of the filler material.

5. It flows into the joint space and a solid joint is formed after cooling

Advantages of Brazing

1. It is easy to learn.

2. It is possible to join virtually any dissimilar metals.

3. The bond line is very neat aesthetically.

4. Joint strength is strong enough for most non-heavy-duty type of application.

Disadvantages of Brazing

1. Brazed joints can be damaged under high temp.

2. Brazed joint require a high degree of cleanliness.

3. The joint colour is often different from that of the base metal.

Welding: - Welding may be defined as the metallurgical joining of two metal pieces

together to produce essentially a single piece of metal. Welding is extensively used in the



fabrication working which metal plates, rolled steel sections, casting of ferrous materials are

joined together. It is also used for repairing broken, worn out, or defective metal part.

Principle of welding A welding is a metallurgical process in which the junction of the two

parts to be joined are heated and then fused together with or without the application of

pressure to produce a continuity of the homogenous material of the same composition and

characteristics of the part which are being joined.

Types of welding

Welding are classified in to two type

• Pressure welding

• Fusion welding

In Pressure welding the parts to be joined are heated only up to the plastic state and then

fused together by applying the external pressure. Ex: forge welding, resistance welding

In Fusion welding which also known as non-pressure is welding, joints of the two parts are

heated to the molten state and allowed to solidify.

Ex: arc welding, gas welding.

Arc welding: - The arc welding operates under the principle that when two conductor of an

electric circuit are touched together momentarily and then instaneously separated slightly,

assuming that there is sufficient voltage in the circuit to maintain the flow of current, an

electric arc is formed. Concentrated heat is produced throughout the length of the arc at a

temperature of about 5000 to 6000°C. In arc welding, usually the parts to be welded are

wired as one pole of the circuit, and the electrode held by the operator forms the other pole.

When the arc is produced, the intense heat quickly melts the work piece metal

which is directly under the arc, forming a small molten metal of the electrode is

carried over by the arc to the molten metal.



Pool of the work piece. The molten metal in the pool is agitated by the action of the

arc, thoroughly mixing the base and the filler metal. A solid joint will be formed

when the molten metal cools and solidifies. The flux coating over the electrode produces

an inert gaseous shield surrounding the arc and protects the molten metal from oxidizing

by coming in contact with atmosphere.

Arc welding machine

Both AC and DC are used for arc welding. For AC arc welding a step down

transformer is used. It receives AC supply between 200 to 440V and transforms it to

required low voltage of 80 to 100V. A high current of 100 to 400A is suitable for arc

welding.

In DC arc welding work piece is connected to positive pole of DC generator and the

electrode to the negative pole in order to melt greater mass of metal in the base metal, this

setup is called straight polarity When the heat required is less in the base metal then the

polarity is reversed Due to this option in DC arc welding it is possible to melt many metals In

AC there is no choice of polarity since the current changes every cycle.

Arc welding electrodes

There are two types of electrodes that are used in arc welding

(A) Consumable electrodes

(B) Non- consumable electrodes

Consumable electrodes are the electrodes which also melts along with the work piece and

fill the joint



Consumable electrodes could be either bare or coated. When bare electrodes are used

globules of the molten metal while passing from the electrodes absorb oxygen and nitrogen

from atmosphere Which gets trapped in the solidifying weld metal and thereby decreases the

strength of the joint Electrodes are made up of soft steel or alloy steel The coating consists of

chalk, starch, Ferro manganese and binding agents.

Coated electrode facilitates:

(a) Protection of molten metal from oxygen and nitrogen by providing a gaseous shield

around the arc

(b) To establish and maintain the arc throughout the welding

(c) The formation of the slag over the joint thus prevents from rapid cooling

(d) Addition of alloying element

Non- consumable electrodes

When these are used, an additional filler material is also required Advantage in using this

electrode is that amount of metal deposited can be controlled which is not possible in other

type of electrode.

Resistance welding: - This type of welding employs the principles of both the pressure and

fusion welding methods. It consist of heating of the Parts to be welded are heated up to the

plastic state and joined by applying mechanical pressure. Heating is done by passage of

heavy localized electric current, the current flowing from one part of joint to other encounters

a high resistance and temp increases. This method is employed for fastening thin metal sheets

and wires.

Gas welding: - It is a fusion welding, in which a strong gas flame is used to raise the

temperature of the work piece to melt them. As in the arc welding, a filler metal is used to fill

the joint. The gases that can be used for heating are

(i) Oxygen and acetylene

(ii) Oxygen and hydrogen.

Oxy-acetylene gas mixture is most commonly used in gas welding

Oxy-acetylene welding

When Right proportions of oxygen and acetylene are mixed in the welding torch and then

ignited. The flame produced is called as the oxy-acetylene flame. The temperature attained

in this welding is around 32000C hence has an ability to melt all commercial metals.



Types of oxy-acetylene flames

The types of flames depends on the gas ratio i.e. ratio of the parts of oxygen to the

parts of the acetylene Depending on the gas ratio following flames are obtained.

(i) Neutral flame

(ii) Oxidizing flame

(iii) Reducing flame (carburising flame).

(i) Neutral flame:-

A neutral flame is obtained by supplying equal volume of oxygen and

acetylene

It consists of a small whitish inner cone surrounded by sharply defined

blue flame

Most of the gas welding is done using the neutral flame

(ii) Oxidizing flame

This is obtained by supplying excess of acetylene in the gas ratio

It has 3 cones, an inner white cone ,surrounded by an intermediate

whitish cone known as “ intermediate flame feather” and a bluish envelope

flame

This flame is used for welding alloy steels, cast iron, aluminium



(iii)Reducing flame:-

This is obtained when there is excess of oxygen, gas ratio

It appears to be similar to that of neutral flame but the inner white cone

flame is shorter than that of neutral flame

This flame is generally used in metal cutting rather than welding since

weld metal gets oxidized

Advantages of oxy-acetylene welding

1. Most versatile process of welding with wide use in various manufacturing process

2. Low cost of the equipment and low cost of maintenance of the equipment

3. Because of separate heat source and filler metal the control can be exercised on

the rate at which the filler metal deposits.

4. The rate of heating and cooling is slow. This help in retaining the structural homogeneity.

5. The equipment is portable and multi-functional because, apart from gas welding, it can

also be used in torch brazing, braze welding, preheating and post heating.

Disadvantages

1. Difficult to attain low cost target while joining heavy section.

2. Handling and storage of gases not an easy job.

3. It takes long time for the flame to heat up the metal piece than compared to the arc

welding.

4. Possible hazards due to explosion of gases.



Difference between Brazing, Soldering and Welding:



MODULE – 5

REFRIGERATION, AIR-CONDITIONING

Refrigeration, Air-Conditioning: Refrigerants: properties of refrigerants, list of commonly

used refrigerants. Refrigeration – Definitions – Refrigerating effect, Ton of Refrigeration, Ice

making capacity, COP, Relative COP, unit of Refrigeration. Principle and working of vapour

compression refrigeration and vapour absorption refrigeration: Principles and applications of

air conditioners, Room air conditioner.

Refrigeration:

It is defined as the process of removing heat from a substance under controlled

conditions and reducing and maintaining the temperature of a body below the temperature of

its surroundings by the aid of external work.

In a Refrigerator, power is to be supplied to remove the heat continuously from the

refrigerator cabinet to keep it cool at a temperature less than the atmospheric temperature.

Refrigerant:

The medium or working substance that continuously extracts heat from the space

within the refrigerator which is to be kept cool at temperature less than atmospheric by

rejecting heat to atmosphere is called refrigerant.

Refrigeration concepts:

1. Heat flows from a system at higher temperature to a system at lower temperature.

2. Fluids absorb heat, change from liquid phase to vapour phase and condenses back to liquid

while

By giving off heat.

3. The boiling and freezing temperatures of fluid depends on its pressure.

4. Heat can flow from a system at lower temperature to a system at higher temperature only

with

The aid of external work.

Unit of Refrigeration:

The capacity of a refrigeration system is expressed in tons of refrigeration, which is

the unit of refrigeration.

A ton of refrigeration is defined as the quantity of heat absorbed in order to form one

ton of ice in 24 hours when the initial temperature of the water is 0°C.

In S.I. System,

1 Ton of Refrigeration = 210 kJ/min

= 3.5 kW



Coefficient of Performance (COP): The performance of a refrigeration system is expressed by a factor known as the

coefficient of performance.

The COP of a refrigeration system is defined as the ratio of heat absorbed in a system

to the work supplied.

Mathematically: COP=Q/W

Where

Q = Heat Absorbed or Removed (kW)

W = Work supplied (kW)

Refrigerating effect:

The rate at which the heat is absorbed in a cycle from the interior space to be cooled.

Ice making capacity:

The capacity of a Refrigerating system to make ice beginning from water (at water

temperature) to solid ice. It is usually specified by kg/hr.

Relative COP

It is defined as the ratio of Actual COP to the Theoretical COP of a refrigerator.

Relative COP= Actual COP/Theoretical COP.

REFRIGERANT: A Refrigerant is medium it continuously extracts the heat from the space within the

refrigerator which is to be kept cool at temperatures less than the atmosphere and finally

rejects to it to the surroundings.

The most commonly used refrigerants are given below:

1) Ammonia:-Ammonia as a refrigerant is employed in refrigerators operating on the

absorption principles. Because of its high latent heat (1300 kJ/kg at -15°C) and low specific

volume (0.509mVkg at -15°C) it produces high refrigeration effects even in small

refrigerators.

Since ammonia will not harm the ozone, it is environmental friendly. It is widely used

in cold storage, ice making plants, etc.

It is toxic, flammable, irritating and food destroying properties makes it unsuitable for

domestic refrigerators.

2) Sulphur dioxide: - Earlier Sulphur dioxide was one of the most commonly used

refrigerants in domestic refrigerators. Although it has better thermodynamic properties, it has

low refrigerating effect and high specific volume, therefore large capacity high speed

compressors are required.

Since it combines with water and forms sulfurous and sulphuric acids which are

corrosive to metals, the refrigerators using Sulphur dioxide as refrigerant are seldom used.



3) Carbon dioxide: - The efficiency of the refrigerators using carbon dioxide refrigerant is

low. Therefore it is seldom used in domestic refrigerators, but is used in dry ice making

plants. It is colourless, odourless, non-toxic, non-inflammable and non-corrosive.

4) Methyl Chloride:-Methyl chloride was used earlier in domestic and small scale industrial

refrigerators. Since it will burn under some conditions and slightly toxic, is not generally

used.

5) Freon:-Freon group of refrigerants is used almost universally in domestic refrigerators.

These refrigerants are colourless, almost odourless, non-toxic, non-inflammable, non-

explosive and non-corrosive, Freon-12 and Freon-22 are the two Freon refrigerants

commonly used in domestic refrigerators and air conditioners.

Although these refrigerants are being now used extensively in the refrigerators and

the air conditioners, it has been found that these refrigerants posing a major threat to the

global environment through their role in the destruction of the ozone layer.

PROPERTIES OF A GOOD REFRIGERANT

Thermodynamic properties:

1) Boiling Point: - The Temperature at which a liquid boils and turns to vapour.

An ideal refrigerant must have low boiling temperature at atmospheric pressure.

2) Freezing Point: The Temperature at which a liquid turns into a solid when cooled.

An ideal refrigerant must have a very low freezing point because the refrigerant should not

freeze at low evaporator temperatures.



3) Evaporator and Condenser Pressure: - In order to avoid the leakage of the atmospheric

air and also to enable the detection of the leakage of the refrigerant, both the evaporator

and condenser pressures should be slightly above the atmospheric pressure.

4) Latent Heat of Evaporation: - latent heat of fusion it is heat required to change a

substance from a solid (ICE) to a liquid (WATER) or vice versa while the latent heat of

vaporization from a liquid (water) to a gas (steam) or vice versa.

The latent heat of evaporation must be very high so that a minimum amount of refrigerant

will accomplish the desired result, in other words, it increases the refrigeration effect.

Physical properties:

1) Specific Volume:-The specific volume of the refrigerant must be very low. The lower

specific volume of the refrigerant at the suction of the compressor reduces the size of the

compressor.

2) Specific heat of liquid and vapour:-A good refrigerant must have low specific heat

when it is in liquid state and high specific heat when it is vapourised. The low specific

heat of the refrigerant helps in sub-cooling of the liquid a high specific heat of the vapour

helps in decreasing the superheating of the vapour. Both these desirable properties increase

the refrigerating effect.

3) Viscosity:-The viscosity of a refrigerant at both the liquid and vapour states must be very

low as improves the heat transfer and reduces the pumping pressure.

Chemical properties:

1) Non-toxicity refrigerant:-A good refrigerant should be non-toxic, because any leakage

of the toxic refrigerant increase suffocation and poisons the atmosphere.

2) Corrosiveness:-A good refrigerant should be non-corrosive to prevent the corrosion of

the metallic parts of the refrigerators.

3) Chemical Stability: - An ideal refrigerant must not decompose under operating

conditions.

Other properties:

1) Coefficient of Performance:-The coefficient of performance of a refrigerant must be

high so that the energy spent in refrigeration will be less.

2) Odour:-A good refrigerant must be odourless, otherwise some foodstuff such as meat,

butter, etc. loses their taste.

3) Leakage Tests:-The refrigerant must be such that any leakage can be detected by simple

tests.

4) Action with Lubricating Oil:-A good refrigerant must not react with the lubricating

oil used in lubricating the parts of the compressor.



PARTS OF A REFRIGERATOR

To accomplish the task of producing the cooling effect, a refrigerator must consist of

the following main parts,

1. Evaporator

2. Circulating System (compressor or pump)

3. Condenser

4. Expansion Device

1) Evaporator:-In the evaporator (heart of the refrigerator) liquid refrigerant is evaporated

by the absorption of heat from the refrigerator cabinet in which the substances which have to

be cooled are kept. The evaporator consists of simply metal tubing which surrounds around

the freezing and cooling compartments to produce the cooling effect required for freezing ice

or lowering the temperature of perishables placed in the cooling compartment. Since it

produces the cooling effect it is also sometimes called as cooling coil or freezer coil.

2) Circulating System: - The circulating system comprises of the mechanical devices such

as compressors or pumps necessary to circulate the refrigerant to undergo the refrigeration

cycle. They increase the pressure and therefore, the temperature of the refrigerant. Generally

these devices are driven by the electric motors. The electrical energy input to the motor is the

energy input to the refrigerators.

3) Condenser: - A condenser is an appliance in which the heat from the refrigerant is

rejected at higher temperature to another medium, usually the atmospheric air. In a condenser

the refrigerant vapour gives off its latent heat to the air and consequently condenses into

liquid so that it can be recirculated in the refrigeration cycle. The latent heat of the refrigerant

that is given off in the condenser comprises mainly of the heat absorbed in the refrigerator

cabinet and the heat developed due to compression.



4) Expansion Device: - An expansion valve serves as a device to reduce the pressure and

temperature of the liquid refrigerant before it passes to the evaporator. The liquid refrigerant

from the condenser is passed through an expansion valve where it reduces its pressure and

temperature.

TYPES OF REFRIGERATION SYSTEMS The refrigeration systems are mainly divided into two types, they are

1) Vapour Compression Refrigerator (VCR)

2) Vapour Absorption Refrigerator (VAR)

1) Vapour Compression Refrigerator (VCR): Most commonly used refrigerants in the

vapour compression refrigerator is dichlorodifluoromethane, popularly known as Freon 12,

or R12.

Vapour compression refrigerator consists of an evaporator made of coiled tubes

installed in the freezing compartment of the refrigerator and connected to the suction side of

the compressor and a throttle valve. The delivery side of the compressor is connected to a

condenser which in turn is connected to a throttle valve.

WORKING: The refrigerant at low pressure and low temperature passing in the evaporator

coiled tubes and absorbs the heat from the contents in the freezing compartment and

evaporates. This in turn lowers the temperature in the freezing compartment. The evaporated

refrigerant at low pressure from the evaporator, is drawn by a compressor which compresses

it to higher pressures so that the saturation temperature of the refrigerant corresponding to the

increased pressure is higher than the temperature of the cooling medium (atmospheric air) in

the condenser, so that the high pressure and high temperature vapours can reject heat in the

condenser and be ready to expand in the throttle valve to the lower evaporator pressures

again.



The high pressure high-temperature refrigerant vapour from the compressor flows to

the condenser where it gives off its latent heat to the atmospheric air. As a result of the loss

of latent heat in the condenser, the refrigerant condenses.

The high pressure condensed liquid refrigerant approximately at room temperature

now flows to the throttle valve in which it expands to a low pressure and then passes to the

evaporator coils for recirculation once again. The throttling expansion of the refrigerant

lowers its pressure and temperature and at the same time causes it to partly evaporate. Hence

the refrigerant coming out of the expansion valve will be a very wet vapour and at a very low

temperature which will be around -10°C. This wet vapour now passes to the evaporator coils

where it absorbs its latent heat and then recirculated to repeat the cycle continuously.

Thus, heat is continuously extracted by the contents of the refrigerator in the

evaporator and rejected in the condenser to the atmospheric air. This will keep the contents of

the refrigerator at the required lower temperature. The required low temperature is

maintained in the refrigerator by a thermostat switch which switches on and off the



compressor motor by a relay as and when the temperature either falls below, or rises above

the required temperature.

2) Vapour Absorption Refrigerator (VAR):

Most commonly used refrigerant in the vapour absorption refrigerator is ammonia. In

this refrigerator, the ammonia liquid vapourised in the evaporator coils absorbing the latent

heat from the freezing compartment thus keeping it cool and subsequently gives off heat

when it condenses in a condenser. Then ammonia liquid from the condenser is heated in a

heater to vapourised it.

Thus the absorption system makes use of heat energy to change the state of the

refrigerant required in the cycle. A pump is used to circulate the refrigerant in the cycle.

WORKING: Vapour absorption refrigerator consists of an absorber, a circulation pump, and

heat exchanger, heater cum separator, condenser, expansion valve and evaporating coiled

tubes. Dry ammonia vapour is dissolved in the weak ammonia solution of ammonia- water

contained in the absorber, which will produce a strong ammonia solution. Since, cold water

(absorbent) has the capacity to absorb ammonia vapour from the evaporator is dissolved in

the weak ammonia solution thus produces strong ammonia solution.

A circulation pump draws the strong ammonia solution from the absorber and pumps

it to the heat exchanger, where it is warmed by the warm weak ammonia solution which is

flowing back from the heater-separator. From the heat exchanger, the warm high pressure

strong ammonia solution is passed to the heater-cum-separator provided with the heating

coils.



The heating coils in the heater-separator heats the strong ammonia solution. Heating

of the high pressure strong ammonia solution will drive out the ammonia vapour from it and

consequently the solution in the heater-separator becomes weak which in turn flows back to

the heat exchanger where it warms up the strong ammonia solution passing through it. The

high pressure ammonia vapour from the heater-separator now passes to a condenser, where it

is condensed. The high pressure ammonia liquid is now expanded to a low pressure and low

temperature in the throttle valve.

The high pressure ammonia vapour from the heater-separator now passes to a

condenser, where it is condensed. The high pressure ammonia liquid is now expanded to a

low pressure and low temperature in the throttle valve. The low pressure condensed ammonia

liquid at low temperature is passed onto the evaporator coils provided in the freezing

compartment, where it absorbs the heat and evaporates.

The low pressure ammonia vapour from the freezing compartment is passed again to

the absorber where it is reabsorbed by dissolving in water. The strong low pressure ammonia

solution from the absorber is again re-circulated to repeat the cycle continuously.



Differences B/w Vapour Compression and Vapour Absorption Refrigerator:

AIR CONDITIONING

Providing a cool indoor atmosphere at all times regardless of weather conditions

needed either for human comfort or industrial purposes by artificially cooling, humidifying

or dehumidifying, cleaning and recirculating the surrounding air is called air conditioning.

The artificial cooling of air and conditioning it to provide maximum comfort to human

beings is called comfort air conditioning. Similarly, providing a controlled atmosphere

required in some engineering manufacturing and processing is called industrial air

conditioning.

Although the cooling and conditioning of the air required for comfort air conditioning

is more or less same in any part of the globe, the industrial air conditioning needs to be

designed to suit the specific individual application.



ROOM AIR-CONDITIONER

Room air-conditioner mainly consists of an evaporator, condenser, compressor, two

fans one each for the evaporator and condenser units usually driven by the single motor,

capillary, etc. It is generally mounted on a window sill such that the evaporator unit is inside

the room and the condenser part projecting outside the building.

WORKING: The high-pressure, low-temperature liquid refrigerant from the condenser is

passed to the evaporator coils through the capillary tube where it undergoes expansion. The

low-pressure, low temperature liquid refrigerant passes through the evaporator coils.

The evaporator-fan continuous draws the air from the interior space with in the room

through an air filter by forcing it to pass over the evaporator coils. The air from the interior

passing over the evaporator coils is cooled by the refrigerant which consequently evaporates

by absorbing the heat from the air.

The high-temperature evaporated refrigerant from the evaporator is drawn by the

suction of the compressor which compresses it and delivers it to the condenser. The high-

pressure, high-temperature refrigerant vapour now flows through the condenser coils.



The condenser-fan draws the atmospheric air from the exposed side-portions of the

air conditioner which is projecting outside the building into the space behind it and

discharges to pass through the Centre section of the condenser unit over the condenser coils.

The high-pressure, high-temperature refrigerant passing inside the condenser coils condenses

by giving off the heat to the atmospheric air. The cooled high-pressure refrigerant from the

condenser passes through the capillary tube where it undergoes expansion and is again re-

circulated to repeat the cycle continuously.

HUMIDITY Humidity is defined as the moisture content present in the atmosphere. The

atmosphere always contains some moisture in the form of water vapour. The maximum

amount depends on the atmospheric conditions. The amount of vapour that will saturate the

air increases with a rise in temperature.

For example, at 4°C, 1000 kg of moist air contains a maximum of 4.4 kg of water

vapour. At 38°C, the same amount of moist air contains a maximum of 18 kg of water

vapour. As is evident that when the atmosphere is saturated with water, the level of

discomfort is high because the evaporation of perspiration.

Humidity can be specified in three different ways.

Absolute humidity:-The absolute humidity is defined as the, weight of water vapour

contained in a given volume of air. It is expressed in grams of water vapour per cubic metre

of air.

Specific humidity:-The specific humidity is defined as the ratio of weight of water vapour to

the total weight of air. It is expressed in grams of water vapour per kilogram of air.

Relative humidity:-The relative humidity is defined as the ratio of the actual vapour content

of the air to the vapour content of air at the same temperature when saturated with water

vapour.

Temperature-Humidity Index (THI):-The temperature-humidity index (THI), also called

discomfort index, expresses in numerical values the relationship between comfort or

discomfort temperature and humidity. It provides an apparent temperature, or how hot the air

feels. For example, an air temperature of 38°C and relative humidity of 60 percent produces

an apparent very hot temperature or THI, or 54°C. It is felt that THI index of 20°C provides a

comfortable atmosphere.

When a controlled atmosphere is required in air conditioning, the humidity of the air is

varied. When dry air is required, it is usually dehumidified by cooling or by dehydration. In

the latter process the air is passed through adsorptive chemicals such as silica gel. Air is

humidified by circulation through water baths or sprays.



CENTRALIZED AIR CONDITIONING: - Centralized air conditioning systems, widely

employed in theatres, offices, stores, restaurants, public buildings, etc., provide the controlled

atmosphere by heating, cooling and ventilation. The centralized air conditioning systems

include refrigerating units, blowers, air ducts and a plenum chamber in which the air from the

interior of the building is mixed with outside air. In such installations, cooling and

dehumidifying are done during summer months and regular heating systems are used during

winter.

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