http://procom.chonbuk.ac. kr 1 lecture notes on thermodynamics 2008 chapter 8 exergy prof. man y....
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Lecture Notes on Thermodynamics 2008Chapter 8 Exergy
Prof. Man Y. Kim, Autumn 2008, ⓒmanykim@chonbuk.ac.kr, Aerospace Engineering, Chonbuk National University, Korea
http://procom.chonbuk.ac.kr
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Exergy : Work Potential• Work=f ( initial state, path, final state)
• Exergy of Kinetic and Potential Energies
To maximize the work, reversible process and final dead states are necessary
dead state dead state dead state
Kinetic Energy :
2 2kex ke V Potential Energy : pex pe gz
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Reversible Work and Irreversibility• Total Energy = Exergy + Unavailable Energy
• Surrounding Work : surr 0 2 1W P V V• Useful Work : surr 0 2 1uW W W W P V V• Reversible Work : revW
If the final state is dead state, reversible work becomes exergy
• Irreversibility : rev,out ,outuI W W ,in rev,inuI W Wor for energy production devices : rev uW W for energy consuming devices : rev uW W
• Second Law Efficiency,
th
IIth,rev
for heat engine
IIrev
COPCOP
for refrigerator and heat pump
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Exergy Change• Nonflowing (Closed System) Exergy
in out systemE E d Q WE dUHere,
, 00 0 b usefulPd P P d P dW W P dV V + V V
0
0 001HE HE
T TW Q Q Q Q T dS
T TQ W T dS
, , 0 0total useful HE b usefulW W W dU P d T dSV
, 0 0 0 0 0total usefulW U U P T S SV V
• Flow Exergy 0 0flowx Pv P v P P v
2
0 0 0 2V
h h T s s gz
2
0 0 0 0 0 02flowing fluid nonflowing fluid flow
Vx x x u u P v v T s s gz P P v
2
0 0 0 0 0 2mV
X U U P T S S mgzV V
2
0 0 0 0 0 2V
u u P v v T s s gz
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Exergy Transfer by Heat, Work, and Mass• Exergy Transfer by Heat
01heat
TX Q
T
• Exergy Transfer by Work
surr
work
W WX
Wfor boundary workfor other forms of work
• Exergy Transfer by Mass
massX m
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Decrease of Exergy Principle• Decrease of Exergy Principle 2 1 0isolated isolated
X X X
• Exergy Destruction 0 0destroyed genX T S• Exergy Balance for a Closed System
• Exergy Balance for a Control Volume , , 2 1heat work mass in mass out destroyed CV
X X X X X X X
• Reversible Work 1 2revW m
in out destroyed system heat work destroyed systemX X X X X X X X
0
0 2 1 0 2 11 k genk
TQ W P T S X X
TV V
0
0 01 system systemk gen
k
d dXTQ W P T S
T dt dt
V
00 2 1 0 2 11 k gen
k in out
TQ W P m m T S X X
TV V
00 01 CV CV
k genk in out
T d dXQ W P m m T S
T dt dtV
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Homework #8Solve the Problems 8–1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, 11C, 13C, 14C
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