Question

If entropy never decreases than how come when we calculate it in an ideal Rankine cycle, the entropy is shown to decrease (even if you observe it on a T-s diagram) after the fluid has gone through the condenser???

Answer 1

If fluid is going through a condenser then you're not working in a closed system. Entropy always increases in a closed system, but that doesn't mean it can't decrease in an open system where it may have external forces acting on it

Answer 2

Entropy can decrease in part of an isolated system but will increase in other parts leaving the total entropy of the system increased.

Answer 3

Thanks, that makes sense. So I suppose that if the fluid running through the condenser releases heat out into a lake, the entropy of the lake increases?