Heat engines & refrigerators worksheet with answers

A heat engine takes in 2400 kJ of heat from a hot reservoir and rejects 1800 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A heat engine takes in 2700 kJ of heat from a hot reservoir and rejects 1620 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

A heat engine receives heat from a source at 450 °C and rejects heat to the surroundings at 40 °C. Its actual thermal efficiency is 40%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A heat engine works between a hot reservoir at 800 °C and a cold reservoir at 25 °C. It takes in 1100 kJ of heat. Find the most work W_max it could possibly produce.

A refrigerator keeps its cold space at 2 °C in a kitchen at 25 °C, removing heat from the cold space at 5 kW. Find the minimum power input Ẇ_min.

A Carnot heat engine receives 20 kW of heat from a source at 1000 °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 -25 °C and also rejects heat to the surroundings at 27 °C. Find the rate Q̇_L at which heat is removed from the freezer.