Heat engines & refrigerators worksheet with answers

A heat engine takes in 2900 kJ of heat from a hot reservoir and rejects 1885 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 4.93 kW while its compressor uses 2.9 kW of power. Find the rate Q̇_H at which it rejects heat to the kitchen.

A heat engine receives heat from a source at 700 °C and rejects heat to the surroundings at 30 °C. Its actual thermal efficiency is 52%. 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 700 °C and a cold reservoir at 5 °C. It takes in 700 kJ of heat. Find the most work W_max it could possibly produce.

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 15 °C. Both engines produce the same work. Find T_m in °C.

A refrigerator keeps its cold space at 4 °C in a kitchen at 25 °C, removing heat from the cold space at 1 kW. Find the minimum power input Ẇ_min.