This Demonstration shows a Carnot cycle operating either as a heat engine or a heat pump, with finite temperature differences between the hot and cold reservoirs and the high and low temperatures of the Carnot cycle, respectively. The entropy changes for the reservoirs (
) and the overall entropy change
are calculated. When the temperature differences between the reservoirs and the engine/pump are nonzero, the total entropy change is positive. The entropy change of the engine/pump, which is at steady state, is zero. All energies and entropy changes are per unit time, since these are continuous processes, but the time scale is arbitrary. The cycle efficiency
is calculated for the heat engine, and the coefficient of performance (
) is calculated for the heat pump. As the temperature difference between the reservoirs and the engine/pump increases, the efficiency and the coefficient of performance decrease. For the heat engine,
is held constant as the temperature differences change. For the heat pump,
is held constant as the temperature differences change.