Applied Thermodynamics for Mechananical Engineering:

Heat Engine:

It is a device a machine which converted heat energy into mechanical work.

Absolute pressure = Atmospheric pressure± Gauge pressure

Absolute temperature = Temperature in C + 273

Heat transfer, Q = m .C .(T2 – T1) in kJ

Atmospheric pressure = 1.01325 bar

=760 mm of Hg

Standard temperature = 15 C = 288K

Standard pressure = 760 mm of Hg = 101.325 kN/m2

For air : Cp =1.005 kJ/kgK Cv = 0.718 kJ/kgK

Ɣ = 1.4

For water : Cp = 4.19 kJ/kgK

Characteristic gas equation : p.V = m.R.T

General gas equation : p.V/T = C

First law of Thermodynamics : Q = W+ΔU kJ

p.V = C (Boyle’s law)

V/T = C (Charle’s law)

Gas constant : R= 0.287 kJ/kgK

Universal gas constant = 8.314 J / kg mole K

Constant volume process =Iso- chloric

Constant pressure process = Iso- baric

Constant Temperature process = Iso- thermal

Law of conservation of Energy:

It states that, energy can neither be created nor destroyed, but it may be

converted from one form into another form.

Zeroth law of Thermodynamics:

It states that, when two systems are separately in thermal equilibrium

with a third system, then they themselves are in thermal equilibrium with each

other.

First law of Thermodynamics:

It states that, when a system undergoes a cycle,the network transfer is equal

to the net heat transfer.

Second law of thermodynamics:

1. Kelvin planck statement:

2. Clausius statement

Kelvin planck statement:

It is impossible to construct a heat engine working on a cyclic process ,

whose only purpose is to convert all the heat energy supplied to it into an equal

amount of work.

Clausius statement:

Heat can flow from a hot body to a cold body without any help. But heat

cannot flow from a cold body to a hot body without any external work

Thermodynamic cycles:

Carnot cycle (constant temperature cycle)

Otto cycle (constant volume cycle)

Diesel cycle

Joule or Brayton cycle (constant pressure cycle)

Dual combustion cycle

Rankine cycle

Reversible cycle:

A device which operates on a reversed cycle is known as heat pump.

Mean effective pressure:

The mean effective pressure of a cycle or heat engine is the average

pressure acting on the piston during the working stroke. It is given by the mean

height of the p-V diagram. It is expreesed in N/ m²

Diagram factor (Card factor)

Diagram factor is the ratio of area of actual indicator diagram to the area of

theoretical Indicator digarm.

Heat engine:

Internal combustion engine

External combustion engine

Internal combustion engine:

In internal combustion engines, the combustion of fuel takes place inside

the engine cyclinder.

External combustion engine:

In external combustion engines, the combustion of fuel takes place outside

the working cylinder.

Major components of an internal combustion engine:

Cylinder block

Cylinder head

Cylinder liners

Crankcase

Oil sump

Piston

Piston rings

Connecting rod

Crankshaft

Camshaft

Valves

Valve actuating mechanism

Fuel supply system in petrol (S.I) engines:

Storage tank

Fuel tank

Fuel filter

Carburettor

Fuel pumps:

Mechanical pump

Electrical fuel pump

Carburettors:

A carburetter is a device, which vaporizes the fuel &mixes it with the

air. The process of vapourizing the fuel & mixing it with air in a carburetor is

called carburation.

Requirements of a carburetor:

It should atomize & vaporize the fuel

It should prepare a mixture of petrol & air in correct properties

It should supply the fuel air mixture to the engine

It should measure & supply the proper quantity &

Propotion of air & fuel under all conditions of engine operations such as

temperature, speed & load

It should maintain a small reserve of fuel at a constant head

It should withstand vibrations & jerks

Types of Carburettor:

1. Simple Carburettor

2. Solex Carburettor

Simple Carburettor:

It is consists of float chamber, Throttle valve, Mixing chamber,

Venturi, Choke or Stranglar, Float.

Solex Carburettor:

It is consists of Float, Main jet, Venturi, Emulsion tube, Air

correction jet, Spraying nozzels, Butterfly valve, Float disc, Starter petrol

jet, Starter air jet, Cold starting passage, Bi-starter lever, Pilot jet, Air

bleeded orifice, Volume control screw, Idle port, Slow speed operating,

Pump injector, Pump lever, Pump jet, Pump inlet valve, Well

Fuel air ratio:

Air- fuel ratio plays an important role in an engine. Mixing of less

fuel with the same amount of air gives lean or weak mixture.The metering

rod in the carburetor measures the amount of fuel flowing into the mixing

chamber.

Types of System:

1. Open System(Control Volume)

2. Closed System(Control Mass)

3. Isolated System

4. Homogeneous System

5. Heterogeneous System

Open system:

In this type of system mass&energy both can cross the boundry of the

system.

Ex :

Air compressor

Turbine

Pump

Boiler

Closed System:

Energy can cross the bountry but not the mass.

Ex:

Gas enclosed in piston cylinder assembly

Dry cell

Isolated System:

Mass & energy doth cannot cross the boundry of

the system . It is completely uninfluenced from the surroundings. It has fixed

mass & Energy.

Examples;

1.Thermoflask

2.Universe

Homogeneous System:

A System consisting of a single phase is called a homogeneous system.

Hetrogeneous System:

A System which consist more than one place at a time is called a

heterogeneous system.

Thermodynamic Equilibrium:

A System is said to be in a state of thermodynamic equilibrium when

no change in any

macroscopic property is registered , if the system is isolated from its

surroundings.

Types:

1. Mechanical Equilibrium.

2. Chemical Equilibrium.

3. Thermal Equilibrium.

Mechanical Equilibrium:

There is no unbalanced force within the system itself & also between

the system & its surroundings.

Chemical Equilibrium:

There is no chemical reaction within the system& no transfer of matter

from one part of the system to another.

Thermal Equilibrium:

There is no temperature difference parts of the system or between the

system & its surroundings.

State:

When all the properties of a system have definite values, the system is said

to exist at a definite state.

Path:

Any operation in which one or more of the properties of a system changes is

called a change of state.

Process:

When the path is completely specified, the change of state is called a

process.

Cycle:

A thermodynamic cycle is defined as a series of two or more processes for

which the final state is identical with the initial state.