Heat engines & refrigerators worksheet with answers

A refrigerator removes heat from its cold space at a rate of 2.47 kW while its compressor uses 1.3 kW of power. Find the rate Q̇_H at which it rejects heat to the kitchen.

A heat engine takes in 4400 kJ of heat from a hot reservoir and rejects 2640 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A heat engine works between a hot reservoir at 400 °C and a cold reservoir at 35 °C. Find the highest possible thermal efficiency η_max.

A heat engine receives heat from a source at 450 °C and rejects heat to the surroundings at 10 °C. Its actual thermal efficiency is 37%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A heat pump keeps a house at 20 °C while it is -10 °C outside, delivering 11 kW of heat to the house. 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 25 °C. Both engines have the same thermal efficiency. Find T_m in °C.