In a Carnot engine the net entropy changein a cycle is zero. But in an irreversible engine operating between two temperatures the net entropy change in a cycle is positive. As I have understood, this means the irreversible engine tends to lose more heat at lower temperature than the Carnot engine. Why is it so?
[Physics] Why is the net entropy change of an irreversible engine positive
carnot-cyclereversibilitythermodynamics
Best Answer
Net entropy change means entropy change of the world (world means system plus environment). Carnot cycle is a reversible cycle. For a reversible cycle, world entropy change is zero. Because both of system and environment return to their initial states when cycle is completed. But, for an irreversible cycle, world entropy change (net entropy change) isn't equal to zero. Although the system returns to its initial state, but the environment doesn't. So, net entropy change won't be zero and according to Increase in Entropy Principle, it will be positive.