Heat engines & refrigerators worksheet with answers

A heat engine takes in 5000 kJ of heat from a hot reservoir and rejects 3500 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 8.6 kW while its compressor uses 2 kW of power. Find the rate Q̇_H at which it rejects heat to the kitchen.

A heat engine works between a hot reservoir at 800 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

A heat engine receives heat from a source at 300 °C and rejects heat to the surroundings at 10 °C. Its actual thermal efficiency is 35%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A refrigerator keeps its cold space at 5 °C in a kitchen at 28 °C, removing heat from the cold space at 4.5 kW. Find the minimum power input Ẇ_min.

A Carnot heat engine receives 70 kW of heat from a source at 850 °C and rejects heat to the surroundings at 27 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at -10 °C and also rejects heat to the surroundings at 27 °C. Find the rate Q̇_L at which heat is removed from the freezer.