Heat engines & refrigerators worksheet with answers

A heat engine takes in 2200 kJ of heat from a hot reservoir and rejects 1320 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

A refrigerator removes heat from its cold space at a rate of 1.28 kW while its compressor uses 0.4 kW of power. Find the rate Q̇_H at which it rejects heat to the kitchen.

A reversible refrigerator keeps a cold room at -10 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 35 °C. Find the rate Q̇_H at which it rejects heat.

A heat engine works between a hot reservoir at 800 °C and a cold reservoir at 5 °C. Find the highest possible thermal efficiency η_max.

A heat pump delivers 17.5 kW of heat to a heating system at 55 °C, taking heat from a source at 7 °C. Its actual COP is 60% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 950 °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.