The Need for Entropy in Finite-Time Thermodynamics and Elsewhere

Carefully specifying the entropy flow and entropy generation in a system is essential when optimizing its performance. Here we mention that in an ensemble some copies may seemingly violate the second law of thermodynamics, which is OK if on average entropy is produced. We focus on which quantity is being optimized and the need for controls to achieve an optimum. And we emphasize the importance of the defining boundary of what is considered the system; vastly different optima will result for different definitions. Finally, we show the effect of different heat transfer laws as well as the type of working fluid on the entropy production and thus the optimal performance of a system.