不可逆热机的热机效率与循环方向的关系

根据热力学第二定律的克劳修斯说法和熵判据论证不可逆热机的η=- W/ Q1 与循环方向有关 .不可逆热机作正向循环时 ,可用热机效率来描述其功热转换关系 ,结论是η正向 ,可逆 >η正向 ,不可逆 .这表明 :在正向循环中 ,可逆循环热机的热转换为功的比率大于不可逆循环热机 .不可逆热机作逆向循环时 ,应当采用制冷系数来描述其功热转换关系 ,所得结论是β可逆 >β不可逆 .这表明 :可逆循环制冷机单位功提取的热大于不可逆循环制冷机 ;如果仍然采用热机效率来描述其功热转换关系 ,则所得的结论应当是η逆向 ,可逆 <η逆向 ,不可逆 .这表明 :在逆向循环中向高温热源输送相同的热 Q1 的前提下 ,可逆热机消耗的功 W可逆 少于不可逆热机消耗的功 W不可逆 .在证明卡诺定理时 ,不可逆热机只能作正向循环 ,不能令其作逆向循环 .

Relationship Between the Efficiency of Heat Engine and Cyclic Direction of the Irreversible Heat Engine

The relationship between Z=-W/Q₁ of the irreversible heat engine and its cyclic direction is proved according to Clauius statement of second law of thermodynamics and entropy criterion.When the irreversible heat engine runs on forward circulation,the conversion of work into heat (and vice versa) can be indicated by the efficiency of the heat engine,and the conclusion is Z_f,r>Z_f,i.It shows that the ratio of heat transformed into work by a reversible heat engine is larger than the ratio by irreversible heat engine in forward circulation.While the irreversible heat engine runs on backward circulation,the conversion relationship of the work and heat should be indicated by refrigerator coefficient of U_r>U_i.It enunciats that a reversible refrigerator takes out more heat than an irreversible refrigerator in each work cycle.If the conversion relationship at backward circulation should also be indicated by the efficiency of the heat engine,the result is Z_b,rb,i.The physical meaning is that a reversible heat engine needs less work than an irreversible heat engine does when they pump the same heat to the hot reservoir on backward circulation.While proving Carnot theorem,the irreversible heat engine can only run on forward circulation,but not on the opposite.