SlideShare uma empresa Scribd logo
1 de 14
Second Law EfficienciesSecond Law Efficiencies
andand
Exergy Change of a SystemExergy Change of a System
Both heat engines have the same thermal efficiency. Are they
doing equally well?
Because B has a higher TH, it
should be able to do better.
Hence, it has a higher maximum
(reversible) efficiency.
The second law efficiency is a measure of the performance of a
device relative to what its maximum performance could be
(under reversible conditions).
Second law
efficiency for
heat engine A
For heat engine B, ηII = 30%/70% = 43%
The second law efficiency is 100 percent for all reversible devices.
Second Law EfficienciesSecond Law Efficiencies
• For heat engines =For heat engines = ηηthth//ηηth,revth,rev
• For work - producing devices = WFor work - producing devices = Wuu/W/Wrevrev
• For work – consuming devices = WFor work – consuming devices = Wrevrev/W/Wuu
• For refrigerators and heat pumps =For refrigerators and heat pumps =
COP/COPCOP/COPrevrev
• WWrevrev should be determined using the sameshould be determined using the same
initial and final states as actual.initial and final states as actual.
• And for general processes =And for general processes =
Exergy recovered/Exergy supplied =Exergy recovered/Exergy supplied =
1 – Exergy destroyed/Exergy supplied1 – Exergy destroyed/Exergy supplied
Second Law EfficienciesSecond Law Efficiencies
• For explanations of whatFor explanations of what
these terms mean for athese terms mean for a
particular device, see textparticular device, see text
page 401page 401
Example 7-6 Second law efficiency of resistance heaters.
Thermal efficiency is 100%. However, COP of a resistance
heater is 1.
What is the COPHP,rev for these conditions? = 1/(1-TL/TH)
It works out to be 26.7
so second law eff. is
COP/COPrev = 1/26.7
or .037 or 3.7%
See now why resistance
heating is so expensive?
Exergy of a fixed mass or closed system. For a reversible
process, the system work:
δW = PdV = (P – P0)dV + P0dV = δWb,useful + P0dV
For the system heat through a
reversible heat engine:
δWHE = (1 - T0/T) δQ
= δQ – T0/T δQ
= δQ – (-T0dS) which gives:
δQ = δWHE – T0dS
Plug the heat and work
expressions into:
-δQ – δW = dU and integrate
to get:
Wtotal useful = WHE + Wb,useful
=(U–U0) + P0(V–V0) – T0(S–S0)
= W = X (exergy)
Exergy Change of a Closed SystemExergy Change of a Closed System
• ΔΔX = (UX = (U22 - U- U11) + P) + P00(V(V22 - V- V11) – T) – T00(S(S22 - S- S11) + m() + m(۷۷22
22
--
۷۷11
22
) +mg(z) +mg(z22 - z- z11))
• Can also do it on a per-mass basis,Can also do it on a per-mass basis, ΔφΔφ == ΔΔX/m.X/m.
• The exergy change of a system is zero if theThe exergy change of a system is zero if the
state of the system or of the environment doesstate of the system or of the environment does
not changenot change
– Example – steady-flow system.Example – steady-flow system.
• The exergy of a closed system is either positiveThe exergy of a closed system is either positive
or zero.or zero.
Even if T<T0 and/or P<P0 the exergy of the system is positive.
In flowing systems, you also have flow energy.
The exergy of flow energy is the useful work that would be
delivered by an imaginary piston in the flow (xflow = Pv – P0v.
Just like with energy, with
exergy you can replace the
u’s with h’s and get the
exergy of a flowing system.
Just like we use θ for the
energy of a flowing system,
we use the Greek letter psi,
ψ, for the exergy of a flowing
system.
Example 7-7 Work Potential of Compressed Air in a Tank.
Assume ideal gas and ke and pe negligible.
Can calculate mass by ideal gas law. Exergy equation:
X1 = m[(u1-u0) + P0(v1-v0) – T0(s1-s0) +V1
2
/2 + gz]
Why? Then use ideal gas law relations and
T1 = T0 to get X1.
Exergy Change During a Compression. Change in exergy
equation for flow systems:
Δψ = (h2 – h1) – T0(s2 – s1) + (V2
2
– V1
2
)/2 + g(z2 – z1)
Now, with the two states given, find
h’s and s’s and calculate Δψ.
This represents the minimum work
required to compress the refrigerant
between these two states.
This also represents the maximum
amount of work you can get from
expanding this gas again between
the same two states.

Mais conteúdo relacionado

Mais procurados

Exergy analysis - a tool for sustainable technology - in engineering education
Exergy analysis - a tool for sustainable technology - in engineering educationExergy analysis - a tool for sustainable technology - in engineering education
Exergy analysis - a tool for sustainable technology - in engineering education
Patrick VanSchijndel
 
Chapter 10 Powerpoint
Chapter 10 PowerpointChapter 10 Powerpoint
Chapter 10 Powerpoint
Mrreynon
 

Mais procurados (20)

There's more to energy than joules
There's more to energy than joulesThere's more to energy than joules
There's more to energy than joules
 
Simulation of the effects of turbine exhaust recirculation
Simulation of the effects of turbine exhaust recirculationSimulation of the effects of turbine exhaust recirculation
Simulation of the effects of turbine exhaust recirculation
 
Availability and irreversibility
Availability and irreversibilityAvailability and irreversibility
Availability and irreversibility
 
available energy ,irreversibility,exchargy
available energy ,irreversibility,exchargyavailable energy ,irreversibility,exchargy
available energy ,irreversibility,exchargy
 
Energy, Heat and Work
Energy, Heat and WorkEnergy, Heat and Work
Energy, Heat and Work
 
Exergy analysis - a tool for sustainable technology - in engineering education
Exergy analysis - a tool for sustainable technology - in engineering educationExergy analysis - a tool for sustainable technology - in engineering education
Exergy analysis - a tool for sustainable technology - in engineering education
 
Entropy
EntropyEntropy
Entropy
 
First law of thermodynamics
First law of thermodynamicsFirst law of thermodynamics
First law of thermodynamics
 
Lecture 15 first law of thermodynamics
Lecture 15   first law of thermodynamicsLecture 15   first law of thermodynamics
Lecture 15 first law of thermodynamics
 
Chapter 6 availability
Chapter 6 availabilityChapter 6 availability
Chapter 6 availability
 
Entropy
EntropyEntropy
Entropy
 
First law of thermodynamics
First law of thermodynamicsFirst law of thermodynamics
First law of thermodynamics
 
Chapter 10 Powerpoint
Chapter 10 PowerpointChapter 10 Powerpoint
Chapter 10 Powerpoint
 
Thermodynamics
ThermodynamicsThermodynamics
Thermodynamics
 
first law of thermodynamics
first law of thermodynamics first law of thermodynamics
first law of thermodynamics
 
Thermodynamics 2
Thermodynamics 2 Thermodynamics 2
Thermodynamics 2
 
Heat work and energy
Heat work and energyHeat work and energy
Heat work and energy
 
Thermodynamics note chapter:4 First law of Thermodynamics
Thermodynamics note chapter:4 First law of ThermodynamicsThermodynamics note chapter:4 First law of Thermodynamics
Thermodynamics note chapter:4 First law of Thermodynamics
 
Basic of thermodynamics section a
Basic of thermodynamics  section aBasic of thermodynamics  section a
Basic of thermodynamics section a
 
Thermodynamics note chapter:5 second law of thermodynamics
Thermodynamics note chapter:5 second law of thermodynamics Thermodynamics note chapter:5 second law of thermodynamics
Thermodynamics note chapter:5 second law of thermodynamics
 

Destaque

Depc A Abusoglu
Depc A AbusogluDepc A Abusoglu
Depc A Abusoglu
Abusoglu
 
Thermodynamic Chapter 4 Second Law Of Thermodynamics
Thermodynamic Chapter 4 Second Law Of ThermodynamicsThermodynamic Chapter 4 Second Law Of Thermodynamics
Thermodynamic Chapter 4 Second Law Of Thermodynamics
Muhammad Surahman
 
Energy Resource Plan
Energy Resource PlanEnergy Resource Plan
Energy Resource Plan
dianalynnray
 
PROJECT DOCUMENT ON EXERGY final
PROJECT DOCUMENT ON EXERGY final  PROJECT DOCUMENT ON EXERGY final
PROJECT DOCUMENT ON EXERGY final
Alekhya Madisetty
 
Cairo 2nd Petrol Lecture 7
Cairo 2nd Petrol Lecture 7Cairo 2nd Petrol Lecture 7
Cairo 2nd Petrol Lecture 7
Esmail Bialy
 
Vibration measurement
Vibration measurementVibration measurement
Vibration measurement
Mark Nelson
 
(E book) thermodynamics fundamentals for applications - j. o'connell, j. ha...
(E book) thermodynamics   fundamentals for applications - j. o'connell, j. ha...(E book) thermodynamics   fundamentals for applications - j. o'connell, j. ha...
(E book) thermodynamics fundamentals for applications - j. o'connell, j. ha...
Christianne Cristaldo
 
Week 13 vibration measurements
Week 13   vibration measurementsWeek 13   vibration measurements
Week 13 vibration measurements
dankerzgatak
 
Thermodynamic Chapter 5 Air Standard Cycle
Thermodynamic Chapter 5 Air Standard CycleThermodynamic Chapter 5 Air Standard Cycle
Thermodynamic Chapter 5 Air Standard Cycle
Muhammad Surahman
 

Destaque (20)

Exergy
ExergyExergy
Exergy
 
Energy and Exergy Analysis of a Country Sectors - Advanced Thermodynamics
Energy and Exergy Analysis of a Country Sectors - Advanced ThermodynamicsEnergy and Exergy Analysis of a Country Sectors - Advanced Thermodynamics
Energy and Exergy Analysis of a Country Sectors - Advanced Thermodynamics
 
Depc A Abusoglu
Depc A AbusogluDepc A Abusoglu
Depc A Abusoglu
 
Exergy analysis of magnetic refrigeration
Exergy analysis of magnetic refrigerationExergy analysis of magnetic refrigeration
Exergy analysis of magnetic refrigeration
 
Cengel ch07
Cengel ch07Cengel ch07
Cengel ch07
 
Cengel ch06
Cengel ch06Cengel ch06
Cengel ch06
 
Thermodynamic Chapter 4 Second Law Of Thermodynamics
Thermodynamic Chapter 4 Second Law Of ThermodynamicsThermodynamic Chapter 4 Second Law Of Thermodynamics
Thermodynamic Chapter 4 Second Law Of Thermodynamics
 
Lect1
Lect1Lect1
Lect1
 
Energy Resource Plan
Energy Resource PlanEnergy Resource Plan
Energy Resource Plan
 
PROJECT DOCUMENT ON EXERGY final
PROJECT DOCUMENT ON EXERGY final  PROJECT DOCUMENT ON EXERGY final
PROJECT DOCUMENT ON EXERGY final
 
Cairo 2nd Petrol Lecture 7
Cairo 2nd Petrol Lecture 7Cairo 2nd Petrol Lecture 7
Cairo 2nd Petrol Lecture 7
 
Vibration measurement
Vibration measurementVibration measurement
Vibration measurement
 
(E book) thermodynamics fundamentals for applications - j. o'connell, j. ha...
(E book) thermodynamics   fundamentals for applications - j. o'connell, j. ha...(E book) thermodynamics   fundamentals for applications - j. o'connell, j. ha...
(E book) thermodynamics fundamentals for applications - j. o'connell, j. ha...
 
02 part7 second law thermodynamics
02 part7 second law thermodynamics02 part7 second law thermodynamics
02 part7 second law thermodynamics
 
Week 13 vibration measurements
Week 13   vibration measurementsWeek 13   vibration measurements
Week 13 vibration measurements
 
Mechanical Vibration
Mechanical VibrationMechanical Vibration
Mechanical Vibration
 
Second law of thermodynamic
Second law of thermodynamic              Second law of thermodynamic
Second law of thermodynamic
 
Vibration measuring instruments
Vibration measuring instrumentsVibration measuring instruments
Vibration measuring instruments
 
Thermodynamic Chapter 5 Air Standard Cycle
Thermodynamic Chapter 5 Air Standard CycleThermodynamic Chapter 5 Air Standard Cycle
Thermodynamic Chapter 5 Air Standard Cycle
 
Magnetic refrigeration Seminar PPT
Magnetic refrigeration Seminar PPTMagnetic refrigeration Seminar PPT
Magnetic refrigeration Seminar PPT
 

Semelhante a 2 law and exergy change

Semelhante a 2 law and exergy change (20)

Introduction
IntroductionIntroduction
Introduction
 
Chap_8_lecture.ppt
Chap_8_lecture.pptChap_8_lecture.ppt
Chap_8_lecture.ppt
 
Unit 2.1 thm
Unit 2.1 thmUnit 2.1 thm
Unit 2.1 thm
 
Heat and thermodynamics - Preliminary / Dr. Mathivanan Velumani
Heat and thermodynamics -  Preliminary / Dr. Mathivanan VelumaniHeat and thermodynamics -  Preliminary / Dr. Mathivanan Velumani
Heat and thermodynamics - Preliminary / Dr. Mathivanan Velumani
 
first law of thermodynamics and second law
first law of thermodynamics and second lawfirst law of thermodynamics and second law
first law of thermodynamics and second law
 
Potter, merle c capitulo 8
Potter, merle c capitulo 8Potter, merle c capitulo 8
Potter, merle c capitulo 8
 
10751259.ppt
10751259.ppt10751259.ppt
10751259.ppt
 
07 heat[1]
07 heat[1]07 heat[1]
07 heat[1]
 
HHO driven CCPP
HHO driven CCPPHHO driven CCPP
HHO driven CCPP
 
Thermodynamics
ThermodynamicsThermodynamics
Thermodynamics
 
Thermodynamics
ThermodynamicsThermodynamics
Thermodynamics
 
2nd law of thermodynamics, entropy
2nd law of thermodynamics, entropy2nd law of thermodynamics, entropy
2nd law of thermodynamics, entropy
 
Unit 2: BASIC MECHANICAL ENGINEERING by varun pratap singh
Unit 2: BASIC MECHANICAL ENGINEERING  by varun pratap singhUnit 2: BASIC MECHANICAL ENGINEERING  by varun pratap singh
Unit 2: BASIC MECHANICAL ENGINEERING by varun pratap singh
 
Thermodynamic_Properties.pdf
Thermodynamic_Properties.pdfThermodynamic_Properties.pdf
Thermodynamic_Properties.pdf
 
Che Module-1.pptx
Che Module-1.pptxChe Module-1.pptx
Che Module-1.pptx
 
Waste Heat Recovery Devices by Varun Pratap Singh
Waste Heat Recovery Devices by Varun Pratap SinghWaste Heat Recovery Devices by Varun Pratap Singh
Waste Heat Recovery Devices by Varun Pratap Singh
 
second law
 second law second law
second law
 
6 thermodynamics.ppt
6 thermodynamics.ppt6 thermodynamics.ppt
6 thermodynamics.ppt
 
chapter07_1_0.ppt
chapter07_1_0.pptchapter07_1_0.ppt
chapter07_1_0.ppt
 
Thermodynamics revision
Thermodynamics revisionThermodynamics revision
Thermodynamics revision
 

Último

Online crime reporting system project.pdf
Online crime reporting system project.pdfOnline crime reporting system project.pdf
Online crime reporting system project.pdf
Kamal Acharya
 
ALCOHOL PRODUCTION- Beer Brewing Process.pdf
ALCOHOL PRODUCTION- Beer Brewing Process.pdfALCOHOL PRODUCTION- Beer Brewing Process.pdf
ALCOHOL PRODUCTION- Beer Brewing Process.pdf
Madan Karki
 
21P35A0312 Internship eccccccReport.docx
21P35A0312 Internship eccccccReport.docx21P35A0312 Internship eccccccReport.docx
21P35A0312 Internship eccccccReport.docx
rahulmanepalli02
 
Final DBMS Manual (2).pdf final lab manual
Final DBMS Manual (2).pdf final lab manualFinal DBMS Manual (2).pdf final lab manual
Final DBMS Manual (2).pdf final lab manual
BalamuruganV28
 
Seizure stage detection of epileptic seizure using convolutional neural networks
Seizure stage detection of epileptic seizure using convolutional neural networksSeizure stage detection of epileptic seizure using convolutional neural networks
Seizure stage detection of epileptic seizure using convolutional neural networks
IJECEIAES
 

Último (20)

NEWLETTER FRANCE HELICES/ SDS SURFACE DRIVES - MAY 2024
NEWLETTER FRANCE HELICES/ SDS SURFACE DRIVES - MAY 2024NEWLETTER FRANCE HELICES/ SDS SURFACE DRIVES - MAY 2024
NEWLETTER FRANCE HELICES/ SDS SURFACE DRIVES - MAY 2024
 
Geometric constructions Engineering Drawing.pdf
Geometric constructions Engineering Drawing.pdfGeometric constructions Engineering Drawing.pdf
Geometric constructions Engineering Drawing.pdf
 
Online crime reporting system project.pdf
Online crime reporting system project.pdfOnline crime reporting system project.pdf
Online crime reporting system project.pdf
 
The battle for RAG, explore the pros and cons of using KnowledgeGraphs and Ve...
The battle for RAG, explore the pros and cons of using KnowledgeGraphs and Ve...The battle for RAG, explore the pros and cons of using KnowledgeGraphs and Ve...
The battle for RAG, explore the pros and cons of using KnowledgeGraphs and Ve...
 
Raashid final report on Embedded Systems
Raashid final report on Embedded SystemsRaashid final report on Embedded Systems
Raashid final report on Embedded Systems
 
SLIDESHARE PPT-DECISION MAKING METHODS.pptx
SLIDESHARE PPT-DECISION MAKING METHODS.pptxSLIDESHARE PPT-DECISION MAKING METHODS.pptx
SLIDESHARE PPT-DECISION MAKING METHODS.pptx
 
ALCOHOL PRODUCTION- Beer Brewing Process.pdf
ALCOHOL PRODUCTION- Beer Brewing Process.pdfALCOHOL PRODUCTION- Beer Brewing Process.pdf
ALCOHOL PRODUCTION- Beer Brewing Process.pdf
 
21P35A0312 Internship eccccccReport.docx
21P35A0312 Internship eccccccReport.docx21P35A0312 Internship eccccccReport.docx
21P35A0312 Internship eccccccReport.docx
 
Lab Manual Arduino UNO Microcontrollar.docx
Lab Manual Arduino UNO Microcontrollar.docxLab Manual Arduino UNO Microcontrollar.docx
Lab Manual Arduino UNO Microcontrollar.docx
 
The Entity-Relationship Model(ER Diagram).pptx
The Entity-Relationship Model(ER Diagram).pptxThe Entity-Relationship Model(ER Diagram).pptx
The Entity-Relationship Model(ER Diagram).pptx
 
Introduction to Arduino Programming: Features of Arduino
Introduction to Arduino Programming: Features of ArduinoIntroduction to Arduino Programming: Features of Arduino
Introduction to Arduino Programming: Features of Arduino
 
Linux Systems Programming: Semaphores, Shared Memory, and Message Queues
Linux Systems Programming: Semaphores, Shared Memory, and Message QueuesLinux Systems Programming: Semaphores, Shared Memory, and Message Queues
Linux Systems Programming: Semaphores, Shared Memory, and Message Queues
 
Final DBMS Manual (2).pdf final lab manual
Final DBMS Manual (2).pdf final lab manualFinal DBMS Manual (2).pdf final lab manual
Final DBMS Manual (2).pdf final lab manual
 
Research Methodolgy & Intellectual Property Rights Series 2
Research Methodolgy & Intellectual Property Rights Series 2Research Methodolgy & Intellectual Property Rights Series 2
Research Methodolgy & Intellectual Property Rights Series 2
 
Seismic Hazard Assessment Software in Python by Prof. Dr. Costas Sachpazis
Seismic Hazard Assessment Software in Python by Prof. Dr. Costas SachpazisSeismic Hazard Assessment Software in Python by Prof. Dr. Costas Sachpazis
Seismic Hazard Assessment Software in Python by Prof. Dr. Costas Sachpazis
 
Interfacing Analog to Digital Data Converters ee3404.pdf
Interfacing Analog to Digital Data Converters ee3404.pdfInterfacing Analog to Digital Data Converters ee3404.pdf
Interfacing Analog to Digital Data Converters ee3404.pdf
 
UNIT-2 image enhancement.pdf Image Processing Unit 2 AKTU
UNIT-2 image enhancement.pdf Image Processing Unit 2 AKTUUNIT-2 image enhancement.pdf Image Processing Unit 2 AKTU
UNIT-2 image enhancement.pdf Image Processing Unit 2 AKTU
 
Dynamo Scripts for Task IDs and Space Naming.pptx
Dynamo Scripts for Task IDs and Space Naming.pptxDynamo Scripts for Task IDs and Space Naming.pptx
Dynamo Scripts for Task IDs and Space Naming.pptx
 
Seizure stage detection of epileptic seizure using convolutional neural networks
Seizure stage detection of epileptic seizure using convolutional neural networksSeizure stage detection of epileptic seizure using convolutional neural networks
Seizure stage detection of epileptic seizure using convolutional neural networks
 
Augmented Reality (AR) with Augin Software.pptx
Augmented Reality (AR) with Augin Software.pptxAugmented Reality (AR) with Augin Software.pptx
Augmented Reality (AR) with Augin Software.pptx
 

2 law and exergy change

  • 1. Second Law EfficienciesSecond Law Efficiencies andand Exergy Change of a SystemExergy Change of a System
  • 2. Both heat engines have the same thermal efficiency. Are they doing equally well? Because B has a higher TH, it should be able to do better. Hence, it has a higher maximum (reversible) efficiency.
  • 3. The second law efficiency is a measure of the performance of a device relative to what its maximum performance could be (under reversible conditions). Second law efficiency for heat engine A For heat engine B, ηII = 30%/70% = 43%
  • 4. The second law efficiency is 100 percent for all reversible devices.
  • 5. Second Law EfficienciesSecond Law Efficiencies • For heat engines =For heat engines = ηηthth//ηηth,revth,rev • For work - producing devices = WFor work - producing devices = Wuu/W/Wrevrev • For work – consuming devices = WFor work – consuming devices = Wrevrev/W/Wuu • For refrigerators and heat pumps =For refrigerators and heat pumps = COP/COPCOP/COPrevrev • WWrevrev should be determined using the sameshould be determined using the same initial and final states as actual.initial and final states as actual. • And for general processes =And for general processes = Exergy recovered/Exergy supplied =Exergy recovered/Exergy supplied = 1 – Exergy destroyed/Exergy supplied1 – Exergy destroyed/Exergy supplied
  • 6. Second Law EfficienciesSecond Law Efficiencies • For explanations of whatFor explanations of what these terms mean for athese terms mean for a particular device, see textparticular device, see text page 401page 401
  • 7. Example 7-6 Second law efficiency of resistance heaters. Thermal efficiency is 100%. However, COP of a resistance heater is 1. What is the COPHP,rev for these conditions? = 1/(1-TL/TH) It works out to be 26.7 so second law eff. is COP/COPrev = 1/26.7 or .037 or 3.7% See now why resistance heating is so expensive?
  • 8. Exergy of a fixed mass or closed system. For a reversible process, the system work: δW = PdV = (P – P0)dV + P0dV = δWb,useful + P0dV For the system heat through a reversible heat engine: δWHE = (1 - T0/T) δQ = δQ – T0/T δQ = δQ – (-T0dS) which gives: δQ = δWHE – T0dS Plug the heat and work expressions into: -δQ – δW = dU and integrate to get: Wtotal useful = WHE + Wb,useful =(U–U0) + P0(V–V0) – T0(S–S0) = W = X (exergy)
  • 9. Exergy Change of a Closed SystemExergy Change of a Closed System • ΔΔX = (UX = (U22 - U- U11) + P) + P00(V(V22 - V- V11) – T) – T00(S(S22 - S- S11) + m() + m(۷۷22 22 -- ۷۷11 22 ) +mg(z) +mg(z22 - z- z11)) • Can also do it on a per-mass basis,Can also do it on a per-mass basis, ΔφΔφ == ΔΔX/m.X/m. • The exergy change of a system is zero if theThe exergy change of a system is zero if the state of the system or of the environment doesstate of the system or of the environment does not changenot change – Example – steady-flow system.Example – steady-flow system. • The exergy of a closed system is either positiveThe exergy of a closed system is either positive or zero.or zero.
  • 10. Even if T<T0 and/or P<P0 the exergy of the system is positive.
  • 11. In flowing systems, you also have flow energy. The exergy of flow energy is the useful work that would be delivered by an imaginary piston in the flow (xflow = Pv – P0v.
  • 12. Just like with energy, with exergy you can replace the u’s with h’s and get the exergy of a flowing system. Just like we use θ for the energy of a flowing system, we use the Greek letter psi, ψ, for the exergy of a flowing system.
  • 13. Example 7-7 Work Potential of Compressed Air in a Tank. Assume ideal gas and ke and pe negligible. Can calculate mass by ideal gas law. Exergy equation: X1 = m[(u1-u0) + P0(v1-v0) – T0(s1-s0) +V1 2 /2 + gz] Why? Then use ideal gas law relations and T1 = T0 to get X1.
  • 14. Exergy Change During a Compression. Change in exergy equation for flow systems: Δψ = (h2 – h1) – T0(s2 – s1) + (V2 2 – V1 2 )/2 + g(z2 – z1) Now, with the two states given, find h’s and s’s and calculate Δψ. This represents the minimum work required to compress the refrigerant between these two states. This also represents the maximum amount of work you can get from expanding this gas again between the same two states.