上海交通大学：《热力学 Thermodynamics（I）》课程教学资源（课件讲义）Lecture 38_Exergy of CV systems

上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 38 Cengel Chapter 8 Exergy-A measure of work potential Spring,5/2/2018 Prof.,Dr.Yonghua HUANG 强 AAALLLAAMAA http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日

Engineering Thermodynamics I Lecture 38 Spring, 5/2/2018 Prof., Dr. Yonghua HUANG Cengel Chapter 8 Exergy – A measure of work potential http://cc.sjtu.edu.cn/G2S/site/thermo.html

Open Systems Exergy Analysis Definition of Useful Work for Open Systems: W mout Surroundings @ToP. Reservoir @Tj Assumptions: ● Surroundings are at fixed To and po System interacts only with surroundings and one or more heat reservoirs 上游充通大 May2,2018 2 SHANGHAI JLAO TONG UNIVERSITY

May 2, 2018 2 Open Systems Exergy Analysis Definition of Useful Work for Open Systems: Surroundings @ To ,po Assumptions: • Surroundings are at fixed To and po • System interacts only with surroundings and one or more heat reservoirs . W . Qj . min . mout B A CV . Qo Reservoir @ Tj

Derivation of exergy balance equation for CV sys. 1st law,energy balance: ”-00t-y号g2n+e叫 v2 out 8 2nd law,entropy balance: 5g-Σ8+2m2m6 dt out Solve entropy balance equation for Q,and then substitute in energy balance equation: -Tou dt out +Σo,⑧+mh++g-zmn+ 2 +g 2 in out 2 out 上游通大学 May2,2018 3 SHANGHAI JLAO TONG UNIVERSITY

May 2, 2018 3 Derivation of exergy balance equation for CV sys. 1 st law, energy balance: 2 nd law, entropy balance: Solve entropy balance equation for Qo and then substitute in energy balance equation: 2 2 CV o j in out j in out in out dE v v Q Q W m h gz m h gz dt 2 2                         CV o j in in out out tot o j j in out dS Q Q m s m s dt T T          CV CV o o j in o in out o out o tot j in out j 2 2 j in out j in out in out dE dS T T Q m T s m T s T dt dt T v v Q W m h gz m h gz 2 2                                        

Derivation of exergy balance equation for CV sys. Useful Work: Solving for work term,and rearranging combining: 咸-yn〔n+分+---+g-r Some of the work may be done by or against the atmosphere and is not useful: tWc=Wct-P。 dVcv dt The definition of useful work is then, wh++g-T-m++g-t 2 ou out destruction -} dEcy-p。 dt Ney+T。dt dScv of exergy due to irreversibilities within dt the system. 上游充通大学 May2,2018 4 SHANGHAI JIAO TONG UNIVERSITY

May 2, 2018 4 Derivation of exergy balance equation for CV sys. Solving for work term, and rearranging & combining: Some of the work may be done by or against the atmosphere and is not useful: The definition of useful work is then, 2 2 act in o out o in out in out o CV CV j o o tot j j v v W m h gz T s m h gz T s 2 2 T dE dS Q 1 T T T dt dt                                    CV use act o dV W W p dt   Useful Work: 2 2 use in o out o in out in out o CV CV CV j o o o tot j j v v W m h gz T s m h gz T s 2 2 T dE dV dS Q 1 p T T T dt dt dt                                       destruction of exergy due to irreversibilities within the system

Useful Work for SSSF Open Systems Open system:Assume SSSF (Steady State Steady Flow n-a+g--a+g- 2o1升a。 Further assumptions: ●SSSF and reversible w艺af-w--名小号g-01-号 上游通大学 May2,2018 5 SHANGHAI JIAO TONG UNIVERSITY

May 2, 2018 5 Useful Work for SSSF Open Systems Open system: Assume SSSF (Steady State Steady Flow ) Further assumptions: • SSSF and reversible 2 2 use,SSSF in o out o in out in out o j o tot j j v v W m h gz T s m h gz T s 2 2 T Q 1 T T                                    2 2 o rev,use,SSSF in o out o j in out j j in out v v T W m h gz T s m h gz T s Q 1 2 2 T                                 