上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 34 Chapter 7 Entropy (Section 7.13) Spring,2017 强 Prof.,Dr.Yonghua HUANG RAn员P http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日
Engineering Thermodynamics I Lecture 34 Spring, 2017 Prof., Dr. Yonghua HUANG Chapter 7 Entropy (Section 7.13) http://cc.sjtu.edu.cn/G2S/site/thermo.html
Entropy rate balance for CV systems Like mass and energy,transferred by streams Closed system +o T →open system special dSev dt ∑m空m rate of rates of rate of entropy entropy entropy change transfer production 上游究通大学 Wednesday,April 19,2017 2 SHANGHAI JLAO TONG UNIVERSITY
Wednesday, April 19, 2017 2 Entropy rate balance for CV systems Like mass and energy, transferred by streams Closed system open system special
Integral form of entropy balance eq.for CV 号空包4 Heat flux time rate of entropy Sv(t) transfer accompanying heat transfer 0 引ar-1(》n+人w-pea）-i velocity 上游充通大 Wednesday,April 19,2017 3 SHANGHAI JIAO TONG UNIVERSITY
Wednesday, April 19, 2017 3 Integral form of entropy balance eq. for CV Heat flux velocity
CV at steady state Steady state: Mass balance: ∑m=∑m Energy balance: 0-a.-成，+区a(a+是+-Σe+号+s Entropy balance: 70 dS= "'dt 汽区 Not conserved!! These equations often must be solved simultaneously. irreversibilities 上游充通大 Wednesday,April 19,2017 4 SHANGHAI JIAO TONG UNIVERSITY
Wednesday, April 19, 2017 4 CV at steady state Steady state: Mass balance: Energy balance: Entropy balance: 0 These equations often must be solved simultaneously. Not conserved!! irreversibilities
1-inlet,1-oulet CV at steady state 0= T ri(s1 -s2)+fev +r ( Similar form as CM sys. m Entropy difference at exit and inlet Entropy transfer Entropy production accompanying heat transfer due to irreversibilities >,=,<0 ≥0 0ev (isentropic) For adiabatic system:S2 -S= if reversible->52-S=0 m 上游充通大学 Wednesday,April 19,2017 5 SHANGHAI JLAO TONG UNIVERSITY
Wednesday, April 19, 2017 5 1-inlet, 1-oulet CV at steady state Entropy transfer accompanying heat transfer >, =, < 0 Entropy production due to irreversibilities ≥0 Similar form as CM sys. For adiabatic system: if reversible 0 (isentropic) Entropy difference at exit and inlet