工程热力学习题--空气压缩制冷循环,大气温度为25

工程热力学习题--空气压缩制冷循环,大气温度为25℃,冷库温度为-10℃,压气机增压比为3,压气机绝热效率为82%,膨胀

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参考附图.根据题意：T1=-10℃=263.15KT3=25℃=298.15Kp2/p1= p3/p4=3所以cp=R*γ/(γ-1)=1004.85 J/(kg•K)=1.00485 kJ/(kg•K)T2/T1=T3/T4=( p2/p1)^( γ-1/γ)=3^(0.4/1.4)=1.368738T2=360.183433KT4=217.828394K另据题意：ηcompressor=82%=wcideal/wcreal=(h2-h1)/(h2’-h1)= (T2-T1)/(T2’-T1)ηexpander=84%= wereal /weideal =(h3-h4’)/(h3-h4) = (T3-T4’)/ (T3-T4)从而可得：T2’=(T2-T1)/ ηcompressor+ T1=381.483455KT4’= T3 -(T3-T4)* ηexpander =230.679851K压气机所需功率：Pcompressor= h2’-h1 =cp(T2’-T1)=118.907372 kJ/kg整个制冷装置消耗的功率：Ptotal= Pcompressor-Pexpander= ( h2’-h1) -(h3-h4’)= cp[(T2’-T1)-(T3-T4’)]=51.109993kJ/kg制冷系数：ε=(T1- T4’)/[( T2’-T3)-( T1-T4’)]=0.638381