Applied Termodynamics 01

8/14/2019 Applied Termodynamics 01

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APPLIED THERMODYNAMICS

FOR

SECOND YEAR / THIRD SEMESTER EEE DEPT.

UNIT I


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BASIC CONCEPTS

INTRODUCTION

Thermodynamics is defined as the branch of science which deals with the

relations between energy and heat. These relations are governed by the laws ofthermodynamics. These laws are based on the principle of energy conversion.

It states that energy can be changed from one form to another but the total energy

remains constant. In other words energy cannot be created or destroyed.

APPLICATIONS OF THERMODYNAMICS

Power plants

IC engines

Turbines

Compressors

Refrigeration

Air-conditioning

UNITS AND DIMENSIONS

All physical quantities are characterized by dimensions. Dimensions of physical

quantities may be defined as the properties in terms of quality not of magnitude by whicha physical quantity may be described. Length (L), area (A)and volume (V)are all different

dimensions which describe certain measurable characteristics of an object, e.g.,

A=L2 and V=L3

The arbitrary magnitudes assigned to the dimensions are called as units.

In other words, a unit is a definite standard by which a dimension is to be measured.

The primary or fundamental dimensions are length L in m, mass m in kg, time in sec andtemperature T in K.

The secondary or derived dimensions are velocity V in m/s, Energy E in J and volume V

in m these are expressed in terms of primary dimensions.

SYSTEM OF UNITS

The most common system of unit is metric system SI, which is also known as theInternational System. In this text, the SI (System International) system of units has been

used.


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Energy:

Energy is defined as the capacity to do work. The various forms of energy are

heat energy, mechanical energy, electrical energy and chemical energy. Unit of energy isNm or Joule (J) and kWh.

1 kWh = 3.6 x 106 J

The energy per unit mass is defined as specific energy whose unit is J/kg.

Force:

Force acting on a body is defined by Newton s second law of motion. Accordingto this law, force is proportional to the product of mass and acceleration. When a force of

one Newton applied to a body having mass of one kilogram, gives it an acceleration ofone m/s. The unit of force is Newton (N).

1 N = l kgm/s

Weight of a body (W) is the force with which the body is attracted to the centre of theearth. It is the product of its mass (m) and the acceleration due to gravity.

i.e., W= mg (Value of g = 9.81 m/s at sea level)

Work:

Work is defined as the work done when the point of application of 1 N force movesthrough a distance of 1m in the direction of the force, whose unit is Joule or Nm. The

amount of work (W) is the product of the force (F) and the distance moved (L), W = FL.

Power:

Power is defined as the rate of energy transfer or the rate of work. The unit of power is

watt (W)

1N m/s= 1J/s =1W

1 MW = 106 Kw

Pressure:

Pressure is defined as the force per unit area exerted whose unit is N/m2 which is also

known as Pascal (Pa) and for larger pressures, kPa (Kilo Pascal) and MPa (Mega Pascal)are used. Other units for pressure not in the SI units but commonly used are bar and

standard atmosphere (atm)

0.1 MPa = 100 kPa = 105Pa 105 N/m = 1 bar

1 atm = 101 .325 kPa = 1.01325 bar


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Mostly pressure of a fluid is measured by gauge which gives pressure relative toatmospheric pressure and is called as gauge pressure. In thermodynamic analysis one is

mostly concerned with absolute pressure which is the pressure exerted by a system on itsboundary.

For pressures above atmospheric

Pabsolute = pgauge + patm

For pressures below atmospheric, the gauge pressure will be negative and iscalled as vacuum.

U-tube manometer which is used to measure pressure, the two arms of the tubeare connected to two containers which are at p and p pressures. The tube is filled with a

fluid having density and h is the difference in the heights of the fluid columns. By thehydrostatics principle,

P1-P2 = hg

Where is in kg/m3 h in m, g in m/s2 and then p1 p2 in N/m2

Fig:1(a). For pressure above atm Fig:1(b). For pressure below atm

Temperature:

Temperature is defined as the degree of coldness or hotness of a body. When heatis added to the body, its temperature increases and when heat is removed from the body,

its temperature decreases.

Temperature is the thermal condition of a body on which its capacity of

transferring heat to or receiving heat from other bodies depends. Thus the temperaturedetermines direction, in which the heat flow will take place,

Units of temperature are degree Celsius, degree Kelvin

Temperature K = Temperature C + 273

Under standard temperature and pressure (STP) conditions the temperature of agas is taken as 15C and the pressure as 760 mm of mercury.


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Under normal temperature and pressure (NTP) conditions the temperature of a gasis 0C and the pressure as 760 mm of mercury.

Specific Heat:

Specific heat of a substance is defined as the quantity of heat required to raise thetemperature of unit mass substance to one degree.

Average specific heat,

Where Q is heat interaction kJ, T is Temperature difference K and m is mass kg.

If the state of the substance is liquid or solid there is only one specific heat. For the caseof gaseous substances there are two specific heats, they are:

1. Specific Heat at Constant Volume:When the volume of the gas is constant the quantity of heat required to raise the

temperature of unit mass of gas to one degree is termed as specific heat of gas at constantvolume which is denoted by Cv

2. Specific Heat at Constant Pressure:

When the heat is supplied at constant pressure the quantity of heat required to raise the

temperature of unit mass of gas to one degree is termed as specific heat of gas constantpressure which is denoted by Cp

CLASSICAL APPROACH

MACROSCOPIC AND MICROSCOPIC APPROACH

The behavior of one matter can be studied from macroscopic and microscopicpoints of view.

v The macroscopic approach is only concerned with overall effect of the individualmolecular interactions.

v The microscopic point of view concerned with every molecule and analysis ofcollective molecular action is carried out by statistical techniques.

For example, pressure is a macroscopic quantity, which is defined as the normalforce exerted by a system against unit area of the boundary, i.e., the pressure exerted on

the vessel is equal to the mean change of momentum of all the molecules exertedperpendicular to unit area of the boundary.

This approach is not related with individual molecular action. This pressure canbe measured by using pressure gauge. The microscopic approach is used to explain some

matter which otherwise difficult to understand by macroscopic approach.


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THERMODYNAMIC SYSTEM AND SURROUNDINGS

A thermodynamic system is a region in space or any matter or specified quantity

of matter within a prescribed boundary on which we concentrate. The other mattersoutside of the boundary are known as surroundings. As shown in Fig.2(a) the system and

surroundings are separated by boundary. The boundary may be real or imaginary one.

The system is classified into three:

Closed System

Open System

Isolated System

Closed System:

In this system, the boundaries are closed so that there is no mass transfer. Butthere may be energy transfer into or from the system, while mass remains constant. This

is also known as control mass. e.g., bomb calorimeter.

Open System:

In this system, the boundaries are not closed and mass and energy transfer maytake place through the opening(s) in the boundary. This is also known as control volume.

e.g., turbines and compressors.

Fig:2(a)A thermodynamic system,(b)Closed system,(c) Open System, (d) Isolated system


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Isolated System:

This system is not affected by surroundings. In this there is no mass or energy

transfer across the boundary of the system.

WORKING MEDIUM:

In most of the devices the working medium is gas or vapor. It is important to

know the properties and behavior of the working medium to observe and analyze theworking of devices.

At various pressures and temperatures the properties of the working fluid can bedetermined by using pure substance concept.

The pure substance is defined as a substance that has a fixed chemicalcomposition, e.g., water, nitrogen, helium and carbon-di-oxide.

A mixture of two or more pure substances is also called as pure substance as long

as the chemical composition is same.A mixture of liquid air and gaseous air cannot be called as pure substance because

the mixture is not chemically homogeneous due to different condensation temperatures ofthe components in air at specified pressure.

THERMODYNAMIC EQUILIBRIUM

A system is said to be in a state of thermodynamic equilibrium if there is nochange in the microscopic properties at all points in the system.

For thermodynamic equilibrium, the following three types of equilibrium

conditions have to be satisfied.

Mechanical Equilibrium:

A system is said to be in a state of mechanical equilibrium if there is nounbalanced force with in the system or between the system and the surroundings.

Chemical Equilibrium:

A system is said to be in a state of chemical equilibrium if there is no chemicalreaction or transfer of matter from one part of the system to another.

Thermal Equilibrium:

A system is said to be in a state of thermal equilibrium if there is no change in anyproperty of the system when the system is separated by a diathermic wall from its

surroundings. Diathermic wall defined as a wall which allows heat to flow.


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STATE, PROPERTIES AND PROCESSES:

State of a system is the condition of the system at any particular moment. It may

be identified by the properties such as pressure, temperature and volume, etc.

The property can be measured while the system is at a state of equilibrium. In any

operation there is a change in system properties which is called the change ofstate.

A series of changes in the system between initial state and final state is called

the path of change of state.

When the path is specified completely the change of state followed by theworking medium as it liberates, transfers, transforms or receives energy is called

as process.

A series of state changes or process undergone by a system such that the finalstate is identical with the initial state is defined as a thermodynamic cycle.

Fig .2.1(a) A process Fig .2.1 (b) A cycleIn order to describe a system it is necessary to know the quantities and

characteristics of the system which are known as properties. The properties areclassified as extensive properties and intensive properties.

Properties which are related to mass are called as extensive orextrinsic properties, e.g., volume, energy, etc. If mass increases thevalue of extensive

Properties will increase the properties which are independent of themass of the system are called as intensive or intrinsic properties,e.g., temperature, pressure, velocity, density, etc.

Extensive properties per unit mass are known as specific extensiveproperties which are nothing but intensive properties, e.g., specific volume,

specific energy, density, etc.


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Properties may also be classified into two types. They are fundamentalproperties and thermodynamic properties.

Properties which are measured directly are called as fundamentalproperties, e.g., pressure, volume, temperature, etc.

Properties which cannot be measured directly but in closed cyclethe working medium is recirculated with in the system. In opencycle the working substance is exhausted to the atmosphere after

the process.

ZEROTH LAW OF THERMODYNAMICS:

The zeroth law of thermodynamics states that if two bodies are in thermal

equilibrium with a third body, then they are also in thermal equilibrium with eachother.

Fig: 3 Concept of Zeroth law

Let us consider the temperature equality concept to three systems say, A,B and as shown in Fig.3. The system A consists of a mass of gas enclosed in a

vessel fitted with a thermometer and the system B is a cold iron body. When Aand B are brought in contact, after some time they attain a common temperature

and are then said to exist in thermal equilibrium.

Now the system is brought into contact with a third system C, again A and

C attain thermal equilibrium, then system B and C will show no further change inproperties when brought into contact. That is system A is in thermal equilibrium

with system B and also separately with system C. Then B and C will be in thermalequilibrium with each other.

This law provides the basis for temperature measurement.


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FIRST LAW OF THERMODYNAMICS

The first law of thermodynamics states that a closed system executing a

cycle in which the initial state and final state are same.

i.e., The net work delivered to the surroundings is proportional to the net heat

taken from the surroundings.

That is heat and work is mutually conversible. Since energy can neither be

created nor destroyed, the total energy associated with energy conservationremains constant.

Mathematically,

Where dw is net work delivered during the process and dq is net heat supplied

during the process.

FIRST LAW APPLIED TO CLOSED SYSTEM

As shown in Fig3.2. let us consider a closed system which undergoes a cycle, in

which x and y is two arbitrary properties of the system.

According to first law of thermodynamics for a cyclic process, algebric

sum of t is proportional to algebric sum of heat transferred.

i.e., Q1-2 is proportional to Q2-1

This is applicable if the system involves more heat and work transfers at

different points on the boundary.

Where Q and W represent infinitesimal elements of heat and worktransfer respectively. As no fundamental distinction between the unit of heat and

the unit of work J can be neglected from the equation.


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Internal Energy:

The energy E is the sum of Kinetic Energy (KE), Potential Energy (PE)

and Internal Energy (U). The internal energy is due to the motion of the moleculesand it changes with change in temperature.

For a non flow and closed system, the kinetic and potential energy termsare zero, and then the energy will be

The term E is the change in internal energy

For an isolated system both Q and W are zero, the change in energy is also zero.

Q= 0; W= 0; E=0

For reversible non flow process the work

DISPLACEMENT WORK

The most common example of mechanical work encountered in

thermodynamic system is that associated with a process in which there is a changein volume of a system under pressure.

Let the volume of the fluid within the moving boundary be v1 and pressure

be p1. In p-v diagram, point-1 represents initial state. If the working mediumexpands and moves the piston to top dead centre (TDC) from bottom dead centre(BDC), the work will be done by the working medium. After expansion at state 2,

pressure is decreased and volume increased. Since the system undergoesexpansion process, it is represented by the curve 1 - x - y - 2 in p-V diagram as

shown in Fig.4


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Fig: 4. Displacement work

The change of state from x to y, a very small change of state in whichpressure is almost constant during the change, then the force acting on the

movable boundary F x = p - V

During this piston moves to a distance dL and the work done = force distance traveled.

dW = pAdL = pdV

where dV= AdL

The total work at the moving boundary is

When the work is done by the system, it is called as positive work. This isrepresented by the sign plus, +W indicated the work done by the system.

e.g., expansion.

When the work is done on the system, it is called as negative work. - Windicates the negative work. e.g., compression.


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PATH FUNCTION AND POINT FUNCTION

A non-flow process is one in which the gas is neither be supplied nor

rejected across the boundary of the system. The system moves from state 1 tostate 2 through two different paths A and B, as shown in Fig 5.

Fig. 5.Path Function

Each curve represents the work for each process, these two paths givestwo different work values even though states 1 and 2 are identical, the work

delivered to the shaft depends upon the particular function, so the work is calledas path function.

The differentiation of path function is inexact or imperfect. But the

thermodynamic properties are point functions, because they depend on the endstates and independent of the path which the system follows. The differentiationof point functions is exact or perfect differentials, e.g., change in pressure p2 p1and change in volume V2- V1.

APPLICATION OF FIRST LAW TO NON - FLOW PROCESS:

NON - FLOW PROCESSES

It is the process in which the substance does not leave the system, but

energy only crosses the boundary in the form of work and heat. Non - flowprocesses are classified under two groups. They are

a. Reversible non-flow processes

b. irreversible non-flow processes.


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REVERSIBLE NON-FLOW PROCESSES (CLOSED SYSTEM):

The following non-flow processes are reversible

1. Constant volume (isochoric) process : V = constant; n =

2. Constant pressure (Isobaric) process : p = constant; n = 0

3. Constant temperature (Isothermal) process : T= constant; n = 1

4. Adiabatic (Isentropic) process : PV = constant; n =

5. Polytropic process : PVn = constant; n=n

Where p is pressure, V is volume, T is temperature, n is index of compression orexpansion and is adiabatic index.

Reversible Constant Volume Process:

When volume remains constant during the execution of a process, the

process is called as constant volume process. As shown in Below the systemcontains unit mass and state one in pV diagram represents the system state before

the heating processes. State 2 represents the state of system after heating process.

Applying the first law of thermodynamics

The rise in heat causes rise in internal energy and loss of heat decreases theinternal energy.


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APPLICATION OF FIRST LAW TO FLOW PROCESS:

Most of the systems which are related to power generation are opensystems in which the mass crosses the boundary of the system, and after doing thework it leaves the system. Flow processes are classified into two types, they are

Steady flow process

Non-steady flow process


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STEADY FLOW PROCESS

A steady flow process is one in which the mass flow rate at the entry andat the exit is constant. At any point in the system the properties of the fluid do not

change with time, e.g., compressor, turbines, nozzles, etc.

Assumptions made in the analysis of a steady flow process are,

1. Mass flow rate through the system remains constant.

2. Composition of fluid is uniform

3. State of the fluid at any point in the system remains constant.

4. Work and heat are the only interaction between the system and surroundings.

STEADY FLOW ENERGY EQUATION

As stated in the law of conservation of energy the sum of total energyexerting the system is equal to the sum of total energy leaving the system. Thus

there is no change in stored energy.

Let m - mass flow rate in kg/s, - absolute pressure in N/m2, v - specific volume

in m3 /kg, V - velocity in m/s, Z - elevation above the datum in m, u - specificinternal energy in J/kg, Q - heat into the system in J and W- work output in J.

Fig: 6.Steady flow process


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Assumptions made are

Mass flow in = Mass flow out

Energy in = Energy out

Total energy in = Total energy out

(Potential energy + Kinetic energy + Internal energy + Heat energy) at entry =(Potential energy + Kinetic energy + Internal energy + Work) at exit

PE1 + KE1 + U1 + Q = PE2 + KE2 + U2 + W

This is the steady flow energy equation and all the energy values are in Watts.

The steady flow energy equation can be written in mass basis as given below.

Hence the energy values are in J/kg

Mass flow in= Mass flow out

m1 = m2

We know m =

Where the density of fluidmass

=volume for unit mass

and

1 1= =

specific volume

1 1 2 2

1 2

A V A V

=


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UNSTEADY FLOW PROCESS

An unsteady flow process is one in which the mass flow rate at the entryand exit of the system is not equal in a given time, and there is no change in

stored energy of the system.

Let Eout Ein be the change in flow energy and E change in stored energy.

Based on first law

SECOND LAW OF THERMODYNAMICS

LIMITATIONS OF FIRST LAW

The first law of thermodynamics states that, heat and work are mutuallyconvertible during any cycle of a closed system.

But in actual practice all forms of energy cannot be changed into work andthe first law does not give any conditions under which conversion of heatinto work is possible. The law does not specify the direction of the process

under consideration. The limitations of first law are discussed below.


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The following examples are based on the first law of thermodynamics andthese processes only proceed in certain direction but not in the reverse

direction.

Let T1 and T2 be the temperatures of two bodies where T1 is

greater than T2 If these bodies are brought in contact with each

other but are separated from surround- rigs, heat will flow from hotbody (T1) to cold body (T2) till the temperature of both bodies areequal. But the reverse process is not possible, i.e., flow of heat

from lower temperature body to higher temperature body.

In an automobile moving at a certain speed, if the brakes are

applied to stop the automobile means, the brakes get hot by theconversion of automobile s kinetic energy into heat.

However, it will be observed that reversal of the process in whichthe hot brakes were to cool off and give back its internal energy to

the automobile, causing it to move on the road. But this is

impossible.

SECOND LAW OF THERMODYNAMICS

KELVIN-PLANK STATEMENT OF SECOND LAW

It is impossible to construct an engine which operates on cycle to receive

heat from a single reservoir and produce net amount of work. Kelvin - Plank

statement related to heat engines.

In other words, no engine operating in cycles can convert all the heat

energy into work, but there will be some loss of heat energy to the surroundings.Thus 100% efficient engine is not possible.


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Fig:7. Possible engine and not possible engine

Possible engine is one in which a part of heat is rejected to the coldreservoir, which is supplied from the hot reservoir and the difference between theheat supplied and heat rejected is equal to work done.

CLAUSIS STATEMENT OF SECOND LAW

Clausis statement is related to refrigerators or heat pumps. The Clausis

statement is expressed as follows:

It is not possible to construct a system that operates in a cycle and

transfers heat from a colder body to a hotter body without the aid of an external

agency. In other words, heat can not flow itself from a colder body to a hotterbody.

Based on this, the hot reservoir at T1 temperature and the cold reservoir at

T2 temperature are shown in Fig: 8. The heat pump which takes mechanical workto transfer heat continuously from sink to source.

Fig:8. External work required for heat flow from sink to source


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PERPETUAL MOTION MACHINE OF SECOND KIND (PMM II)

Perpetual motion machine of second kind is one which operators in a cycle

and delivers an amount of work equal to heat extracted from a single reservoir atan uniform temperature.

Such 100% efficiency violates the second law of thermodynamics asaccording to Kelvin - Plank Statement. It is not possible to construct a machine

which could extract heat from a single reservoir and convert it into equivalentamount of work.

HEAT ENGINE

Heat engine is defined as a machine which is used to convert heat energy

into work in a cyclic process.

The definition of heat engine covers both rotary and reciprocating

machines. The working fluid should undergo cyclic process and periodicallyshould return to its initial state.

Fig: 9. Steam power plant as heat engine

Fig: 9. shows a steam power plant which is an example of heat engine

cycle. In the boiler high pressure steam is generated and the steam expands in theturbine and doing external work W exhaust steam from turbine is condensed in

the condenser thereby releasing heat and the water is pumped back to the boiler tocomplete the cycle.

Thus the boiler, turbine, condenser and the pump separately in a powerplant can not be regarded as heat engine because they are engines since they are

part of the cycle. Combination of these components is a heat engine since theycomplete the cycle.


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EFFICIENCY OF HEAT ENGINE

Performance of a heat engine is obtained by its thermal efficiency which

is the ratio of net work output to heat supplied. A part of heat supplied isconverted into work and the rest is rejected.

Let Q1

be heat supplied, Q2

be heat rejected, Wtbe turbine work and W

pbe pump

work (Fig: 10.)

As per the first law of thermodynamics

Fig: 10. Heat engine

Efficiency of the heat engine

Network output=

Heat supplied


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HEAT PUMP

Heat pump is defined as a device which transfers heat from a low

temperature body to a high temperature body when it is working in a cycle

(Fig:11).

For heat pump the efficiency term is replaced by the co-efficient of

performance (COP) which as an index of performance of heat pump todifferentiate it from heat engine. COP of the pump is given by

(heat pump)

Heating effectCOP =

Work done

Fig: 11. Heat pump

If a heat pump is used to transfer heat from low temperature reservoir T2to high temperature reservoir T1 in order to maintain T2 < T1 then the COP of the

refrigerator is given by

ref

Refrigerating effectCOP =

Work input


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CARNOT CYCLE

The Carnot cycle has four reversible processes, of which two arefrictionless isothermal processes and two frictionless adiabatic processes.

Figure.12 shows the p-V and T-s diagram of the Carnot cycle.

Process 1-2 represents reversible isothermal expansion, Heat Q is supplied

at constant temperature T and this is equal to the work done during theprocess.

Heat supplied

21 1 1

1

VQ = P V ln

V

Process 2-3 represents reversible adiabatic expansion, there is no heattransfer takes place. The work is done at the cost of internal energy. The

temperature becomes T2 at T3

Fig.12 Carnot cycle

Process 3-4 represents reversible isothermal compression in which Q2 heatis rejected isothermally at T2. The air is compressed up to point 4 at

constant temperature.

Heat rejected

Process 4-1 represents reversible adiabatic compression in which thesystem returns back to the initial state and the temperature of air increasesfrom. T2 to T1 There is no heat transfer and work is done on the air.


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Net work done = (Heat supplied) - (Heat Rejected)

Efficiency of Carnot cycle = (Net work done / Heat supplied)

CARNOT THEOREM

The Carnot principles are the two conclusions regard to the thermal

efficiency of ideal and natural (actual) heat engines. They are expressed as

follows:

The efficiency of an actual (irreversible) heat engine is always less thanthe efficiency of an ideal (reversible) heat engine operating between thesame two reservoirs.

All the reversible (ideal) heat engines operating between the same tworeservoirs will have the same efficiency.

CLAUSIS IN EQUALITY

While applying second law of thermodynamics to processes the second

law leads to the definition of a new property called entropy. Entropy is an abstractproperty, and it is difficult to give a physical description of it. The uses of entropy

in common engineering processes provide the best understanding of it. Thesecond law may be stated to be the law of entropy.


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The cyclic integral of dQ/T in above equation is always less than or equal to zero.

Inequivality of Clausis is the basis of the definition of entropy. Entropy is a

nonconserved property by which it differs from energy.

This inequality is valid for all cycles, viz., and reversible or irreversible.

The symbol denotes that the integration is to be performed over the entire cycle.Any heat transfer from or to a system can be considered to consist of differential

amounts of heat transfer then the cyclic integral of dQ/T can be viewed as the sumof all these differential amounts of heat transfer divided by the absolute

temperature at the boundary.

CONCEPT OF ENTROPY

ENTROPY AS A PROPERTY OF A SYSTEM

Entropy of a substance is a thermodynamic property which increases with

the addition of heat and decreases with the removal of heat. Entropy itself cannotbe defined but the change in entropy can be defined in a reversible process, i.e.,

the quantity of he received or rejected divided by the absolute temperature of thesubstance measures the change in entropy.

A small amount of heat dQ is added to the system causing the entropy toincrease by ds and T is the absolute temperature. The change in entropy absolute

temperature.

If the total quantity of heat Q be added to a substance at constant

temperature then the increase in entropy due to the addition of heat is given by

Qds =

T

1 2

Q=

Ts s

From the definition of entropy

dQ = T ds

By integrating the equation the total heat added can be obtained as


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ENTROPY - A POINT FUNCTION

Entropy has got one value for each point of temperature or pressure or

volume. So it is a point function. The change in entropy during a thermodynamicprocess depend only on the initial and final conditions irrespective of the path.

In solving problems the change in entropy is considered with theassumption if the entropy of all substances is zero at the ice-point, i.e., the entropy

is positive if the temperature is above 0C and negative if the temperature isbelow 0C. Entropy is expressed as kJ/kgK, since, it has the dimension of

heat/mass and temperature.

There are many instruments to measure temperature, pressure, etc., but

there no such instruments as yet to measure entropy.

ENTROPY OF A REVERSIBLE CYCLIC PROCESS

Let us consider a system undergoing a reversible process from state 1 tostate along the path A and then from state 2 to the original state 1 along the path B

as shown in Fig.13.

Fig. 13. Reversible cyclic process between two fixed states

CHANGE IN ENTROPY OF A PERFECT GAS

Let m kg of gas carryout a process. At the initial state 1 let the pressure,

temperature, entropy and volume are p1, T1, s1 and V1 respectively. The gas isheated in any manner such that at its final state 2 pressure, temperature, entropy

and volume be p2, T2, s2 and V2 respectively.

From the law of conservation of energy


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This is the change in entropy in terms of volume and temperature. This can beexpressed in terms of pressure and volume by applying gas equation as


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JAYAM COLLEGE OF ENGINEERING AND TECHNOLOGY

DHARMAPURI

DEPARTMENT : EEE

YEAR / SEM : SECOND/ THIRD

SUBJECT : ME1211 / APPLIED THERMODYNAMICS

ASSIGNMENT NO 1

Unit 1 Basic concepts and Laws of Thermodynamics

PART A

1. State first law of thermodynamics?

2. State Zeroth law of thermodynamics?

3. What is meant by Perpetual Motion Machine of first kind ?

4. State the statements of second law of thermodynamics?

5. If pvn=C represents a general thermodynamic process, name the processes when n

has values of 0, 1, and .

6. What are the types of thermodynamic properties?

7. Explain the thermodynamic equilibrium? Explain.

8. What is meant by Perpetual Motion Machine of second kind ?

9. State Carnot s theorem.

10. Define Clausis Inequality.

PART B1. Derive then expression for work and heat during constant volume and constant

pressure process.

2. Derive then expression for work and heat isothermal and isentropic process.

3. Derive the steady flow energy equation.

4. A cycle heat engine operates between a source temperature of 800 C and a sink

temperature of 30 C. What is the least rate of heat rejection per KW net output

of engine?

5. 2 kg of air compressed according to the law pV1.3 = constant from a pressure of

1.8 bar and temperature of 30 C to a pressure of 25.5 bar. Calculate

a) The final volume and temperature.

b) Work done

c) Heat transferred

d) Ch i

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Applied Termodynamics 01