Le due definizioni di rendimento termico

In a previous paper, the same author showed that the usual definition of thermal efficiency of heat engines becomes intrinsically ambiguous when applied to cycles in which the system exchanges heat in both senses with the same thermal reservoir, and proposed two ways in which (in order to resolve this ambiguity) the elementary definition can be precised, called ‘η high’ and ‘η low’. Another author objected that only the first of these definitions is correct, i.e. the one according to which Stirling’s cycle and Carnot’s one have the same efficiency. In this paper a comparison is made between the two definitions previously proposed, from which results that both are in principle admissible, but that the second, i.e. the ‘low’ efficiency, is under many respects preferable.