上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 34 Chapter 7 Entropy (Section 7.13) Spring,4/26/2018 强 Prof.,Dr.Yonghua HUANG 几m是。 http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日
Engineering Thermodynamics I Lecture 34 Spring, 4/26/2018 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 上游气通大粤 April 26,2018 2 SHANGHAI JLAO TONG UNIVERSITY
April 26, 2018 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 Heat flux time rate of entropy Sev(t) transfer accompanying heat transfer 0 w-)+p）-sp1元 velocity 上游充通大 April 26,2018 3 SHANGHAI JIAO TONG UNIVERSITY
April 26, 2018 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.-晚+公e+兰+)-Σ(a-兰+x) Entropy balance: 70 dS= "'dt 汽区 Not conserved!! These equations often must be solved simultaneously. irreversibilities 上游充通大 April 26,2018 4 SHANGHAI JIAO TONG UNIVERSITY
April 26, 2018 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 d (isentropic) For adiabatic system:S2 -S= if reversible->52-S=0 m 上游充通大 April 26,2018 5 SHANGHAI JLAO TONG UNIVERSITY
April 26, 2018 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