1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot...
Transcript of 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot...
![Page 1: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/1.jpg)
1st VS 2nd Laws of Thermodynamics
• Directionofaprocess• Qualitypointofview- Intermsof“Entropy”• Entropygenerationalwaysincreases- Ifnot,itviolates2nd lawofthermodynamics• AprocessincreaseEntropyhigh
à Irreversibilityhigh• AprocessincreaseEntropylow
à Irreversibilitylow• Hotà Cold(O);Coldà Hot(X)
• Energyconservation• Quantitypointofview- Intermsof“Energy”• Energycannotbe createdordestroyed,butitalwaysconserves- Ifnot,itviolates1st lawofthermodynamics• Energyinput– Energy output=Energystored• 100%outputw/oanyloss
ThefirstLaws ThesecondLaws
GENESYSLaboratory
![Page 2: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/2.jpg)
1st law of Thermodynamics
Controlmass(ClosedSystem) Controlvolume(OpenedSystem)
W Q KE PU ED + D = + D + DD ( )mass boundaryW Q KE PEW Q KE PE
UHE E D
D
D + D + = + D +D D
D + D = + D + D
D
IfyoursystemisastationarysystemUW QD + D = D ( )mass boundaryW Q UE
HWE
QD + D + =
D
D
+ D
D
= D
D
Emass=PVMovingboundary(closedSystem)
GENESYSLaboratory
![Page 3: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/3.jpg)
Some Remarks about Entropy1. Processescanoccurina certain directiononly,notinany direction.Aprocessmustproceedinthedirectionthatcomplieswiththeincreaseofentropyprinciple,thatis,Sgen≥0.2. Entropyisnon-conservedproperty,andthereisnosuchthingastheconservation
ofentropyprinciple.
3. Theperformanceofengineeringsystemsisdegradedbythepresenceofirreversibility,andentropygeneration isameasureofthemagnitudesoftheirreversibility'spresentduringthatprocess
GENESYSLaboratory
![Page 4: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/4.jpg)
Week1.GasPowerCyclesI
GENESYSLaboratory
![Page 5: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/5.jpg)
Objectives1. Evaluatetheperformanceofgaspowercyclesforwhichtheworkingfluidremainsagasthroughouttheentirecycle2. Developsimplifyingassumptionsapplicabletogaspowercycles3. Discussbothapproximateandexactanalysisofgaspowercycles4. Reviewtheoperationofreciprocatingengines5. SolveproblemsbasedontheOtto,Diesel,Stirling,andEricssoncycles6. SolveproblemsbasedontheBraytoncycle;theBraytoncyclewithregeneration;andtheBraytoncyclewithintercooling,reheating,andregeneration7. Analyzejet-propulsioncycles8. Identifysimplifyingassumptionsforsecond-lawanalysisofgaspowercycles9. Performsecond-lawanalysisofgaspowercyclesGENESYSLaboratory
![Page 6: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/6.jpg)
Combustor And Cycle
Chemical Energy Thermal Energy Mechanical Energy
Fuel
Low Heat Value
Combustion Mechanical linkage
Heat Power Output
Temperature rise Pressure rise
Rotational torque
Rankine CycleStirling Cycle
Otto Cycle
Diesel Cycle
Brayton CycleJet-propulsion Cycle
Combustor ExternalCombustorInternalCombustor
StirlingEngineSteamEngineDieselEngine(Compression-ignition)GasolineEngine(Spark-ignition)GasTurbineJetEngine
GENESYSLaboratory
![Page 7: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/7.jpg)
Basic Considerations in the Analysis of Power CyclesTheanalysisofmanycomplexprocessescanbereducedtoamanageablelevelbyutilizingsomeidealizations
Theidealizationsandsimplificationscommonlyemployedintheanalysisofpowercyclescanbesummarizedasfollows:1. Thecycledoesnotinvolveanyfriction.Therefore,theworkingfluiddoesnotexperienceanypressuredrop asitflowsinpipesordevicessuchasheatexchangers.2.Allexpansionandcompressionprocessestakeplaceinaquasi-equilibriummanner.3.Thepipesconnectingthevariouscomponentsofasystemarewellinsulated,andheattransferthroughthemisnegligible.4.Neglectingthechangesinkineticandpotentialenergiesoftheworkingfluidisanothercommonlyutilizedsimplificationintheanalysisofpowercycles.GENESYSLaboratory
![Page 8: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/8.jpg)
The Carnot Cycle And Its Value in Engineering• TheCarnotcycleisthemostefficientcyclethatcanbeexecutedbetweenaheatsourceandasink• Itiscomposedoffourtotallyreversibleprocesses:Isothermalheataddition,Isentropicexpansion,Isothermalheatrejection,andIsentropiccompression• Itsthermalefficiency•Example9-1(showthatthethermalefficiencyofaCarnotcycleoperatingbetweenthetemperaturelimitsofTH andTL issolelyafunctionofthesetwotemperature)• TherealvalueoftheCarnotcyclecomesfromitbeingastandard againstwhichtheactualortheidealcyclescanbecompared P-vandT-sdiagramsofaCarnotcycle
H
L
TT
-=1Carnot th,h
GENESYSLaboratory
![Page 9: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/9.jpg)
Air-Standard Assumptions
• Theworkingfluidisair,whichcontinuouslycirculatesinaclosedloopandalwaysbehavesasanidealgas• Alltheprocessesthatmakeupthecycleareinternallyreversible• Thecombustionprocessisreplacedbyaheat-additionprocessfromanexternalsource• Theexhaustprocessisreplacedbyaheat-rejectionprocessthatrestorestheworkingfluidtoitsinitialstate• Airhasconstantspecificheatswhosevaluesaredeterminedatroomtemperature(25oC)ß cold airstandardassumption
GENESYSLaboratory
![Page 10: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/10.jpg)
Entropy Change of Ideal Gases
TvdP
Tdh
T
Pdv Tduds
-=
+=
dTcdhdTcdu
RTPv
p
v
===
v
p
dT dv ds c RT vdT dPc RT P
= +
= -
1
22
1
1
22
112
ln)(
ln)(
P PR
TdTTc
v vR
TdTTcss
p
v
-=
+=-
ò
ò
Thedifferentialentropychangeofanidealgas
Theentropychangeforaprocessobtainedbyintegrating
GENESYSLaboratory
![Page 11: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/11.jpg)
Constant Specific Heats (Approximate Analysis)
2 22 1 avg
1 1
2 2,avg
1 1
, ln ln
ln ln (kJ/kg K)
v
p
T v s s c RT vT P c RT P
- = +
= - ×
2 22 1 avg
1 1
2 2,avg
1 1
, ln ln
ln ln (kJ/kmol K)
v u
p u
T v s s c RT vT P c RT P
- = +
= - ×
Entropychangescanalsobeexpressedonaunitmolebasis
Theentropychangerelationsforidealgasesundertheconstantspecificheatassumption
GENESYSLaboratory
![Page 12: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/12.jpg)
Isentropic Processes of Ideal Gases (Approximate Analysis)
vcR
v vv
TT
v v
cR
TT
÷÷ø
öççè
æ=Þ-=
2
1
1
2
1
2
1
2 lnlnlnln
1, -=Þ=-= kcR
cckccR
vv
pvp
1
2 1
1 2const.
(ideal gas)k
s
T vT v
-
=
æ ö æ ö=ç ÷ ç ÷
è ø è ø1st isentropicrelation
2 22 1 avg
1 1
2 2,avg
1 1
, ln ln
ln ln
v
p
T v s s c RT vT P c RT P
- = +
= -
( )1
2 2
1 1const.
(ideal ga s)
kk
s
T PT P
-
=
æ ö æ ö=ç ÷ ç ÷
è ø è ø 2nd isentropicrelation2 1
1 2const.
(ideal gas) k
s
P vP v
=
æ ö æ ö=ç ÷ ç ÷
è ø è ø 3rd isentropicrelation1
1
constant
constant (ideal gas) constant
k
( -k)k
k
Tv
TPPv
- =
=
=
CompactformsGENESYSLaboratory
![Page 13: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/13.jpg)
Variable Specific Heats (Exact Analysis)
K)(kJ/kg ln1
21212 ×--=-
P PRssss oo
Itisexpressedonaunit-molebasisTheentropychangerelationsforidealgasesunderthevariablespecificheatassumption
ò=T
p TdTTcs
0)(o
oo12
2
1)( ss
TdTTcp -=ò
K)(kJ/kmol ln1
21212 ×--=-
P PRssss u
oo
GENESYSLaboratory
![Page 14: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/14.jpg)
Isentropic Processes of Ideal Gases (Exact Analysis I)
0ln1
21212 =--=-
P PRssss oo
)exp( RsPro
=
1
212 ln
P PRss += oo
÷øö
çèæ
÷øö
çèæ
=-
=
Rs
Rs
Rss
P P
o
o
oo
1
2
12
1
2
exp
expexp
Relativepressure1
2
const.1
2
r
r
s PP
P P
=÷÷ø
öççè
æ
=
2
1
1
2
1
2
2
22
1
11
PP
TT
vv
TvP
TvP
=®=
1
1
2
2
2
1
1
2
1
2
r
r
r
r
PT
PT
PP
TT
vv
==1
2
const1
2
r
r
s vv
vv
=÷÷ø
öççè
æ
=
Relativespecificvolumevr=T/Pr
• Strictlyvalidforisentropicprocessesofidealgasesonly• ThevaluesofPr andvr arelistedforairinTableA-17
GENESYSLaboratory
![Page 15: 1 VS 2nd Laws of Thermodynamicscontents.kocw.net/KOCW/document/2016/chungbuk/kimkibum/2.pdfa Carnot cycle operating between the temperature limits of THand TLis solely a function of](https://reader033.fdocuments.us/reader033/viewer/2022041520/5e2e0bdeb61d553e7540d64a/html5/thumbnails/15.jpg)
Isentropic Processes of Ideal Gases (Exact Analysis II)
• ThevaluesofPr andvr listedforairinTableA-17areusedforcalculatingthefinaltemperatureduringanisentropicprocess
GENESYSLaboratory