s15.2 heat engines and the second law of thermodynamics 2. The efficiency of the heat engines Q W>0 For a cycle: ∠1U=0 total =W=0H -ec s15.2 heat engines and the second law of thermodynamics 的 冷凝器 net 2H-e Q =1 2H 2H 2H5 2. The efficiency of the heat engines QC TC W For a cycle: Q W QH QC U = = − = total ∆ 0 V P W > 0 §15.2 heat engines and the second law of thermodynamics QH QC W1 W2 H C H H C H Q Q Q Q Q Q W = − − = = 1 net ε §15.2 heat engines and the second law of thermodynamics