Heat engines & refrigerators worksheet with answers

A heat engine takes in 4700 kJ of heat from a hot reservoir and rejects 3760 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A refrigerator removes heat from its cold space at a rate of 3.41 kW while its compressor uses 1.1 kW of power. Find its coefficient of performance COP_R.

A heat engine works between a hot reservoir at 750 °C and a cold reservoir at 5 °C. It takes in 1100 kJ of heat. Find the most work W_max it could possibly produce.

A heat engine receives heat from a source at 650 °C and rejects heat to the surroundings at 25 °C. Its actual thermal efficiency is 51%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A refrigerator keeps its cold space at -25 °C in a kitchen at 28 °C, removing heat from the cold space at 1.5 kW. Find the minimum power input Ẇ_min.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 1200 °C and rejects heat to an intermediate reservoir at temperature T_m. Engine B takes all that heat and rejects heat to a reservoir at 20 °C. Both engines have the same thermal efficiency. Find T_m in °C.