meg 201 lecture i & ii

8/7/2019 Meg 201 Lecture i & II

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In Science a type of question often asked is how much? How big? In order to answer such questions it is

important to have systems of measurement which are consistent and understood by all.

DIMENSIONS

Dimension is a property that can be measured such as distance, time, mass, temperature, speed, e.t.c

AUNIT

A unit is a basic division of a measure quantity and it enables one to say how much of the quantity we have.

FUNDAMENTALUNITS

A set of Fundamental Unit is a set of units for physical quantities from which every other unit can begenerated. There are seven basic fundamental Units in the field of Science and Engineering. The units are

listed below;

DERIVEDUNITS

Derived Units are units that are defined by reference to combinations of the Fundamental units.

DIMENSIONS & UNITS


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FUNDAMENTAL UNITS

There are seven basic fundament units in the field of Science and Engineering.:

Physical Quantity Unit

Length(l) Meter(m)

Mass(m) Kilogram(KG)

Time(t) Seconds(s)

Temperature(T) Kelvin (K)

Electric Current (I) Ampere (A)

Luminous Intensity Candela(cd)

Amount of Substance (n) Mole(mol)


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A system of unit is a set of Fundamental units defined for the purpose of measuring all necessary

physical quantities.

There are two major systems of units

1. Metric System

2. British Imperial System

S.I. unit will be used throughout in this course. S.I. unit is The International System of Units.

Adopted by the General Conference of weight and measures in 1960 and consequently endorsed

by the International Organization for Standardization. It is aCoherent System In a Coherent

System, all derived unit quantities are formed by the product or quotient of other unit quantities.

SYSTEM OFUNITS


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FUNDAMENTAL CONCEPTS

The following Fundamental Thermodynamic Concepts to be considered in

this course at this level are:

Systems

Control Volume

Properties and State of a System

Thermodynamic Process

Heat

Work

Pressure

Temperature

Zerothe Law


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THERMODYNAMIC SYSTEM

A system may be defined as a region

in space containing a quantity of

matter whose behaviour is being

investigated. This quantity of matter

is separated from its surrounding by a

boundary which may be a physical

boundary e.g. wall of a vessel.

A system may be defined as a collection

of matter within a prescribed and

identifiable boundary.

The boundaries are not necessarily

inflexible while surrounding is restricted

to those portion of matter external to the

system which are affected by change

occurring within the system

Boundary

Surroundings

Systems


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Boundary

Classification of Thermodynamic Systems

Thermodynamic systems can be classified into two basic: Closed System and

Open System

. Closed System

It is one in which there is no mass

transfer across the boundaries. e.gCombustion chamber of an Internal

combustion engine. It is a system of

fixed mass and identity whose

boundaries are determined by the

space of the matter occupied in it.

. Open System

An open system is one in which there is atransfer of mass of the working substance

across the boundaries. e.g. In a gas

turbine.

Turbine

Outlet

Inlet

Turbine


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CONTROL VOLUME

A control volume is defined as a fixed region in space where

one studies the masses and energies crossing the boundaries

of the region.

The concept of a control volume is very useful in analyzing

fluid flow problems.

Control Volume

1 2


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PROPERTIES & STATE OFA SYSTEM

Properties of a System

All the quantities that identify the State of a system are called Properties.

It is classified into two general groups; Extensive and Intensive Properties

Extensive Properties

The Properties of the system, whose

value for the entire system is equal to

the sum of their values for the

individual parts of the system are

called extensive properties, e.g. total

volume, total mass and total energy of

a system are its extensive properties.

Intensive Properties

The Properties of the system, whose

value for the entire system is not

equal to the sum of their values for

the individual parts of the system are

called intensive properties, e.g.

temperature, pressure and density


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State of a SystemIn all problems in Applied Thermodynamics we are concerned with energy transfers to or

from a system. Thestate of a system (when the system is in thermodynamic equilibrium) is

the condition of the system at any particular moment which can be identified by the statementof its properties, such as pressure, volume, temperature e.t.c. The number of properties

required to describe the system depends upon the nature of the system.

Path of Change ofState

When a system passes through the

continuous series of equilibrium states

during a change of state (from the initial

state to the final state), then it is known as

thepath of change of State.


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THERMODYNAMIC PROCESS

When a system changes its state from one equilibrium state to another equilibrium

state, then the path of successive state through which the system has passed is

known as thermodynamic process.

Thermodynamic or CyclicP

rocessWhen a process or processes are performed on a system in such a way that the

final state is identical with the initial state, it is known as a thermodynamic cycle or

cyclic process.


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HEAT

Heat is a form of energy which is transferred from one body to another body at a lower temperature , byvirtue of the temperature difference between the bodies.

Surroundings

For example when a body A at a certain temperature, say 50C, is brought into contact with a body B at a hightemperature, say 55C, then there will be a transfer of heat from B to A until the temperature of A are equal.

When the temperature of A is the same as the temperature of B, no heat transfer takes place between the bodies andthey are said to be in thermalequilibrium.

Heat is a form of transient energy which can be identified only when it crosses the boundary of a system. It exist

only during transfer of energy into and out of a system.

Heat can never be contained in a body or possessed by a body.

The heat flowing into a system is considered aspositive and heat flowing out of a system is considered negative

Heat can be transferred in three distinct ways, i.e. conduction, convection and radiation

S.I unit for heat is the Joule.

A BThermal

Insulator


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WORK

Mechanical work is defined as theproduct of a force(F) and the distance (l)

moved in the direction of the force.

W = F x l

Work done by the system on its surrounding is considered aspositive work,

while work on the system by its surrounding is considered as negative work.

Work is observed to be energy in transition. It is never contained in a body or

possessed by a body.

S.I unit of work is Nm = 1J


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CONTROL VOLUME

WORKDONE Work done by the fluid on the piston is givenby;

dW = F x dl

= P x A x dl

where A is the area of the piston

A x dl = dv

dW = Pdv

work done by the expanding fluid is;

W (+ve)

System

W(-ve)

Q(+ ve) Q(- ve)

Surrounding

F FFF

dv

Work done at moving boundary in a

Piston-Cylinder


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Quasi-Static or Quasi-equilibrium Process

When the process is carried out in such a way that at every instant, the system derivation from the

thermodynamics equilibrium is infinitesimal, then the process is known as Quasi-Static or Quasi-equilibrium

Process and each state in the process may be considered as an equilibrium state.

iv. Work done at constant volume

V1 = V2 = V

W = 0


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Quiz(10mins)

(1) State four thermodynamic processes (2) Give four similarities between Heat andWork

Solution

1) Thermodynamic Processes are;

Cyclic Process

Isobaric Process

Isothermal Process

Isochoric Process

Polytropic Process

Isentropic Process

Adiabatic Process

2) Similarities between Heat & work

i) Heat and Work are both transient phenomena.The systems do not possess heat or work.

ii) Heat and Work are boundary phenomena .They are observed at the boundary of thesystem.

iii) Heat and Work represent the energy crossingthe boundary of the system.

iv) Heat and Work are path function and hencethey are inexact differentials. They are writtenas Q and W


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Things to read-up

Temperature

Pressure

meg 201 lecture i & ii

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