上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lecture 22 Chapter 5 Mass and Energy Analysis of Control Volume Analysis (Section 5.5) Spring,4/8/2018 强 Prof.,Dr.Yonghua HUANG MAAR http://cc.sjtu.edu.cn/G2S/site/thermo.html
Engineering Thermodynamics I Lecture 22 Spring, 4/8/2018 Prof., Dr. Yonghua HUANG Chapter 5 Mass and Energy Analysis of Control Volume Analysis http://cc.sjtu.edu.cn/G2S/site/thermo.html (Section 5.5)
Transient Transient-not steady,dynamic,a function of time... Examples:startup or shutdown of turbines,compressors... Assumption:SS ©Mass balance dmev ∑m-∑m ↓ [〔()山-()血-（Σj血 -a0-a(）→ mev()-me(0)=∑n:-∑me 上游通大学 mi April 8,2018 2 SHANGHAI JLAO TONG UNIVERSITY
April 8, 2018 2 Transient Transient – not steady, dynamic, a function of time… • Examples: startup or shutdown of turbines, compressors… Assumption : SS Mass balance me
Energy balance for transient process General energy rate balance dEev dt a.-成+∑(a+年-到(+是+密 Integrate from 0>t 2m-o=0.-取+(a）-(a ↓ hmi hme U(d)-Ue(O)=Oev-Wcv+∑mh;-∑mehe Intensive property form? --->No but only when uniform 上游充通大 April 8,2018 3 SHANGHAI JIAO TONG UNIVERSITY
April 8, 2018 3 Energy balance for transient process General energy rate balance Integrate from 0 t Intensive property form? Qcv= mqcv No but only when uniform ??
Example 22.1 charging of a Rigid Tank by Steam Known: P;=1 MPa ·Insulated rigid tank T;=300°C Steam Initially evacuated Steam unsteady Determine: ·T2 m1=0 Assumptions: P2 =1 MPa T2=? ·Uniform flow Qext→0 △PE,△KE→0 CV (a）Flow of steam into an evacuated tank ·Wv→0 上游文通大学 April 8,2018 4 SHANGHAI JIAO TONG UNIVERSITY
April 8, 2018 4 Example 22.1 charging of a Rigid Tank by Steam Known: • Insulated rigid tank • Initially evacuated • Steam • unsteady Determine: • T2 Assumptions: • Uniform flow • Qext 0 • ∆PE, ∆KE 0 • WCV0 CV
Solution P:=1 MPa T,=300°C Steam Initially evacuated >m=0 and mu=0. ·One inlet,no outlet m1=0 P2=I MPa T3=? 0 个 0 0 Un0-Uo)=Q-W,+∑mh-n, (a)Flow of steam into an evacuated tank uniform (Mass energy balance) =m2u2 u2=h; Table A6 P2 1 MPa T2=456.1°C P;=1MPa u2=3051.6 kJ/kg h=3051.6kJ/kg T,=300°C >300℃？--→h=U+ -->u2x 上游充通大 April 8,2018 5 SHANGHAI JIAO TONG UNIVERSITY
April 8, 2018 5 Solution • Initially evacuated m1 = 0 and m1u1 = 0. • One inlet, no outlet 0 0 0 0 =m2u2 uniform Table A6 >300˚C u2x (Mass & energy balance) ??