Example 1.power plant condenser Condensate >Q→0 Steam 0.1 bar 2二 0.1 bar Known:steam vapor 45°C x=0.95 no pressure change Determine: > m and Cooling Cooling water water 20°C 35C Assumptions: Control volume for part(a) ·SS 2 ·ofCV/Surroundings→0 Condensate Steam Wcy =0 △PE,△KE→0 Energy transfer to ● cooling water At states 2,3,4 (liquids) Control volume for part(b) h≈h(T 上游充通大 March 27,2017 6 SHANGHAI JIAO TONG UNIVERSITY
March 27, 2017 6 Example 1. power plant condenser Known: steam vapor no pressure change Determine: • and Assumptions: • SS • of CV/Surroundings0 • • ∆PE, ∆KE 0 • At states 2, 3, 4 (liquids) h ≈ hf (T) 3 1 m m C V 1 Q m Q CV m1 C V W 0 Q0
Solution Mass balance:Separated channels/fluids m1=i2 m3=m4 0.1 bar 45.8C 2 Overall condenser: 4 3 Energy rate balance (SS): U -+a(a++)(++ underlined terms Condensate Steam drop out 0.1 bar 2 0.I bar 45C x=0.95 m3_h1-h2 > 0=i1(h-h)+i3(h3-h4)→ Cooling Cooling rt hs-h3 water water 20°C 35C 上游充通大 March 27,2017 7 SHANGHAI JIAO TONG UNIVERSITY
March 27, 2017 7 Solution Mass balance: Separated channels/fluids Overall condenser: Energy rate balance (SS): underlined terms drop out
Solution cont. State 1:two-phase h=h+x(hg-h) 0.1 bar 0.95 P1=0.1bar Sat.Table A-5 45.8℃ 21 =191.83+0.95(2584.7-191.83)=2465.1kJ/kg U States 2,3,4:compressed/saturated liquid h2≈h(T2)=188.45kJ/kg h3≈h(T3)andh4≈hr(T4) 0 m3 h1-h2 2465.1-188.45 m 36.3 h4-h3 62.7 上游充通大学 March 27,2017 8 SHANGHAI JLAO TONG UNIVERSITY
March 27, 2017 8 Solution cont. State 1: two-phase 1 ( ) f g f h h x h h + - 0.95 p1=0.1bar + Sat. Table A-5 States 2, 3, 4: compressed/saturated liquid
Solution cont. Only condensing stream: Energy rate balance (SS): 0.1 bar v +g 45.8C 2 21 Mass balance (SS):m=riz C underlined terms 0 drop out Cey ri(h2 -h) 2 Condensate Steam =h,-h=18845-2465.1=Q276.7k/e Energy transfer to cooling water my energy is transferred from the condensing steam to the cooling water 上游充通大 March 27,2017 9 SHANGHAI JIAO TONG UNIVERSITY
March 27, 2017 9 Solution cont. Only condensing stream: Energy rate balance (SS): underlined terms drop out energy is transferred from the condensing steam to the cooling water + Mass balance (SS):