aircornot cycle for making subject easy

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Heat Engine introduction

To meet the increasing demand of power, alarge number of power producing deviceshas been developed.

They are classied as

• Indirect energy converters• Direct energy converter

In indirect energy conversion system, thechemical energy of fuel is rst converted

into heat, by burning of fuel and then heatenergy is converted into mechanical energyand then electrical energy with the help ofgenerator



ources of Energy

• ource of energy means material ob!ects thatcontain energy in usable "uantities.• primary energy sources # that derived directly

from natural resources• secondary energy sources # that generated by

man using suitable plant or station byconverting primary energy

• $on renewable energy sources# are thosewhich do not get replenished after theirconsumption

• %enewable energy sources # are those whichrenewed by the nature again and again andtheir supply is not a&ected by rate ofconsumption



ource of heat

• 'ollowing source of heat energy is used for theconversion into mechanical wor(

• )hemical energy # In this the chemical energyof solid, li"uid or gaseous fuels is convertedinto heat energy by combustion of fuels

• *tomic or nuclear energy# The heat energy isreleased by the change in structure of atomicmaterial by fusion e.g. fuel li(e uranium

• Heat energy# The best energy may be directlyobtained from solar radiation or from naturalresources such as wind, geothermal etc.



+rime movers

• * prime movers is a device whichconverts the raw energy of naturalresources into mechanical energy

• * thermal prime movers is a devicewhich converts the low grade heatenergy into high grade wor( energy.How ever the conversion of heat intowor( is restricted according to elvinplan( statement of second law ofthermodynamics.



Heat engine

• * machine which converts heatenergy into mechanical wor( is calledHeat engine.

-r

• * device which can produce wor(continuously which operate on cyclic

process/ at the e0pense of heat inputis called heat engine



assumptions in studying thetheoretical cycle of heat engines

• The wor(ing substance is assumed to be aperfect gas and obeys all the gas laws.

• There is no change in the mass of the wor(ingsubstance.

• *ll the processes are reversible.• Heat is supplied from a source at constant high

temperature.• ome heat is re!ected to sin( at constant low

temperature during the cycle.

• There are no heat losses from the system tosurrounding.

• The specic heats remain constant throughoutthe cycle.



)omponents of heat engine• Heat reservoir# a heat reservoir is dened as the source of

innite heat energy and nite amount of heat absorb or heatre!ected from the source is not a&ect its temperature i.e the

temperature of heat reservoir remains constant.

• * heat reservoir which supply heat is called the heat source

• * heat reservoir which absorbs heat from the system is calledheat sin(.

• E0pander or Turbine# it is a device in which wor(ing 1uid ise0panded and wor( is generated

• )ompressor or +ump# it is a device in which the pressure of

wor(ing 1uid is increase. It may be coupled to e0pander or itmay be connected to separate power source

• 2or(ing 1uid# substance which receives and re!ects heat andundergoes various processes of heat engine cycle is calledwor(ing 1uid



The )arnot cycle#

• adi )arnot a 'rench engineer, proposedthe concept of heat engine wor(ing onreversible cycle called )arnot cycle

• * wor(ing substance receives heat at ahigher temperature and re!ects heat at alower temperature.

• The cycle consists of two isothermal

processes 345 and 647 and two reversibleadiabatic processes 546 and 743.



conti

• This is most important basic cycle becauseit composed of a reversible processes,

• This is the most thermodynamically

e8cient processes, as it gives the conceptof ma0imum thermal e8ciency betweentwo temperature limits.

• )arnot cycle represented as a standard ofperfection and engine can be comparedwith it to !udge the degree of perfection.



cycle

• The wor(ing substance is gas.• +iston4cylinder arrangement is

weightless and friction less.

• Heat transfer ta(es place with the helpof reservoir.• The wall of piston and cylinder is

perfectly insulated.

due to this assumption theanalysis become easy. The wor( done,pec( pressure, pec( temperature andthermal e8ciency based on theoreticalcycle is ma0imum and will be di&erfrom those of actual cycle.



The )arnot )ycle

• Idealized thermodynamic cycle consisting of four reversible processes (any

substance):

Reversible isothermal expansion (1-! "#$constant)

Reversible adiabatic expansion (-%! &$'! "#")

Reversible isothermal compression (%-! "$constant)

Reversible adiabatic compression (-1! &$'! ""#)

1- -% %- -1



Thermal e8ciency of )arnotcycle

• Is given by ed heatreceiv

ed heatreject ed Heatreceivth

−=η

1

2

1

4

33

1

21

log

loglog

V

V

mRT

V

V mRT

V

V mRT −

=



-tto cycle

• The cycle was originally conceived byfranchman named beau de rochas in39:5. The cycle was successfully

applied to an internal combustionengine by Dr. ni(olaus *ugust -tto a;erman engineer in 39:<.

• This cycle is theoretical cycle onwhich the modern petrol engine isbased.



+4= Diagram of -tto cycle



-tto cycle consists of 7reversible cycle

• 345# reversible adiabatic compression of air.+ressure and temperature of air will increase

• 546 #constant volume heat addition furtherrise in pressure and temperature of air

• 647# reversible adiabatic e0pansion of air.+ressure and temperature of air willdecrease. 2or( is developed during process

• 743# )onstant volume heat re!ection.+ressure and temperature of air will restoreto its initial value.



+4= diagram of -tto cycle



*ir standard e8ciency

Is given by heatadded

workdonea =η

( ) ( )

( )23

1423

T T C

T T C T T C

v

vv

−

−−−

=

23

141

T T

T T

−

−

−=

( ) 1

11

−

−=γ

η r

a

( ) 1

11

−

−=∴γ

η r

a



Diesel cycle

• The cycle was conceived by %udolfdiesel, a ;erman engineer, the dieselengine is named after him. The

diesel cycle consist of two adiabaticprocesses 345 and 647, one constantpressure 546 and one constant

volume process 743



Diesel cycle



Diesel cycle

• 345# reversible adiabatic compression of air.+ressure and temperature of air will increase

• 546# heat addition at constant pressure. Duringthis process of pressure of air remain constantand volume and temperature will increase.

• 647# reversible adiabatic e0pansion of air.+ressure and temperature of air will decrease.

• 743# heat re!ectio>n at )onstant volume,pressure and temperature of air will decrease.



Diesel cycle



Diesel cycle• *ir standard e8ciency

( )

−

−−=

−1

111

1 ρ

ρ η

γ

γ r

a

plied heat

workdonea

sup=η

( ) ( )

( )23

1423

T T C

T T C T T C

p

v p

−

−−−

=

( )( )23

141T T

T T

−

−

−=

γ

( )23 T T C Q p s −=

( )14

T T C Q v R −=

R s QQ −=

#eat supplied

#eat re*ected

+or, done per cycle



%an(ine cycle

• In steam power plant heat is released byburning fuel which is ta(en up by water.

• 2ater is converted into steam which is

e0panded in turbine producing mechanicalwor( and then producing electrical energyby generator.

• E0haust steam from turbine is thencondensed in condenser and then pumpedto boiler where it again gets heat and cycleis repeated



%an(ine cycle



T4 Diagram of %an(inecycle

)ycle 34546474?43 is saturated ran(inecycle

3@45@46474?43@ is a superheated ran(ine

cycle



%an(ine cycle

•345# the point 3 represents thesaturated steam at boiler pressure.+rocess 345 represents the adiabaticreversible e0pansion of steam in the

steam turbine. During this processe0ternal wor( is developed and thepressure of steam falls from p3 to p5.the point 345@ is same as 345 .

The e0haust vapour at 5 and 5@ isusually in the two phase region.



)ontiA

• 546# this process represents the

constant pressure heat re!ection inthe condenser. The steam comingout from the turbine condensed in

the condenser. During condensationof steam, the pressure is constantand there is a phase change from

steam to water and latent heat ofsteam is carried away by thecirculating water in the condenser.



)ontiA• 647# this process represents the

adiabatic reversible compression offeed water by the pump fromcondenser pressure +6 to steam

generator pressure +7. line 647 isalmost vertical on both the +4= and T4 diagram because the li"uid is

essentially incompressible and thepump is adiabatic reversible



)onti..• 743# this process represents the constant pressure

heat addition in the steam generator. The process 74?represent the supply of heat to bring the sub cooledli"uid 7 to saturated li"uid ?. the constant pressuresection 74? in the steam generator is called aneconomiBer. The 6 and 7 are same on +4= diagram. *sincrease in volume of water during this heating

process is negligible.• The portion ?43 represent heating of saturated water

at constant pressure and temperature till the steamwater completely converts into steam and the section?43 in the generator is called the boiler. +ortion 343 in

the superheat cycle, represents heating of saturatedvapour to superheat vapour, 3 at constant pressure.ection 343 in the steam generator is called a superheater.



E8ciency of ran(ine cycle

• +ump# for reversible adiabatic pumping C>

• ?oiler# heat is supplied and no wor( is done by it

• Turbine# for isentropic e0pansion C>

• )ondenser# heat is re!ected to cooling water

34 hhW p −=

41 hhQ s −=

21 hhW t −=

32 hhQ

R −=

ler pliedinboiheat

put Networkout Rankine

sup=η

( ) ( )

)( 41

3421

hh

hhhh Rankine

−

−−−

=∴η

( )

)( 41

21

hh

hh Rankine

−

−

=∴η



E8ciency of ran(ine cycle

• +ump# for reversible adiabatic pumping C>

• ?oiler# heat is supplied and no wor( is done by it

• Turbine# for isentropic e0pansion C>

• )ondenser# heat is re!ected to cooling water

34 hhW p −=

41 hhQ

s −=

21 hhW t −=

32 hhQ R −=

ler pliedinboiheat

put Networkout Rankine

sup=η

( )( )

)( 41

3421

hh

hhhh Rankine

−

−−

=∴η

( )

)( 41

21

hh

hh Rankine

−

−

=∴η

aircornot cycle for making subject easy

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