上游充通大学 SHANGHAI JIAO TONG UNIVERSITY Engineering Thermodynamics I Lectures 17 Chapter 5 Mass and Energy Analysis of Control Volume Analysis Spring,2017 Prof.,Dr.Yonghua HUANG 强 是a http://cc.sjtu.edu.cn/G2S/site/thermo.html 1日G
Engineering Thermodynamics I Lectures 17 Spring, 2017 Prof., Dr. Yonghua HUANG http://cc.sjtu.edu.cn/G2S/site/thermo.html Chapter 5 Mass and Energy Analysis of Control Volume Analysis
Developing the Energy Rate Balance for a CV Energy is an extensive property Energy enters/leaves CV Mass enters and exits. Energy transfers can occur by heat and work Inlet i Energy Conservation Principal time rate of change of the energy contained within Control the control volume at volume time t W; +8 Exit e net rate at which net rate at which net rate of energy energy is being energy is being transfer into the Dashed line defines transferred in transferred out 十 control volume the control volume boundary by heat transfer by work at accompanying at time t time t mass flow 1-inlet 1-exit CV> 1D flow =Q-+m4+ dt 2 +gzi me ue 2 上降文通大学 Mar/20,Mon,2017 2 SHANGHAI JLAO TONG UNIVERSITY
Mar/20, Mon, 2017 2 Developing the Energy Rate Balance for a CV Energy is an extensive property Mass enters and exits Energy enters/leaves CV Energy Conservation Principal 1-inlet 1-exit CV + 1D flow
Work for a CV Energy transfers can occur by heat and work dE。=Q-w Control volume dt 2 + 2 + Exit e -Dashed line defines the control volume boundary Net rate of work across the boundary (1)Fluid pressure as mass flow (2)All other work “+” (peAe)Ve-（pA)V; We (p--pressure,A--area,V-velocity) AV riw Specific volume W=Wev+m(p)-m,D四 Mass flow rate Flow work 上游气通大粤 Mar/20,Mon,2017 3 SHANGHAI JLAO TONG UNIVERSITY
Mar/20, Mon, 2017 3 Work for a CV Net rate of work across the boundary (1) Fluid pressure as mass flow (2) All other work Wcv (p--pressure, A--area, V– velocity) “+” “-” Mass flow rate Specific volume Flow work
Different Forms of CV Energy Rate Balance 0- dt 个 W=Wv+m(pve)-m(p） 0 --++)+m+苦+) dt h:convenience dEey dt Lev-Wev+rin hi+ 2 +gi - rite he 2 Multi-stream (General): =a.-+Σa(6++)Σae-兰 dt 上降文通大学 Mar/20,Mon,2017 →Integration 4 SHANGHAI JIAO TONG UNIVERSITY
Mar/20, Mon, 2017 4 Different Forms of CV Energy Rate Balance hi : convenience Multi-stream (General): Integration
Example 17.1 CM vs.CV analysis Known: 0.15 m3 O2 cylinder,Initially t1=38 C,p=0.55 MPa,V=0.15m3. Pressure release valve:automatically open when p 0.7 MPa, ·Heating the O2: Find:2@To2=285℃ [R=260 J/(kgK);cy=657 J/(kgK);c=917 J/(kgK)] =0.15m 14138C 2 告285C 055M明CY 名0.7N亚 CV g0.7p 3 上游究通大学 Mar/20,Mon,2017 5 SHANGHAI JIAO TONG UNIVERSITY
Mar/20, Mon, 2017 5 Example 17.1 CM vs. CV analysis Known: • 0.15 m3 O2 cylinder, Initially t1=38 ℃, p1= 0.55 MPa, V=0.15m3 . • Pressure release valve: automatically open when p > 0.7 MPa, • Heating the O2 . Find: Q @ TO2 = 285 ℃ [R=260 J /(kg·K)；cV = 657 J/(kg·K)；cp= 917 J/(kg·K)]