Heat engines & refrigerators worksheet with answers

A heat engine takes in 3800 kJ of heat from a hot reservoir and rejects 2280 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 3.52 kW while its compressor uses 0.8 kW of power. Find its coefficient of performance COP_R.

A heat engine works between a hot reservoir at 625 °C and a cold reservoir at 10 °C. Find the highest possible thermal efficiency η_max.

A reversible refrigerator keeps a cold room at -20 °C by removing 1.5 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇_H at which it rejects heat.

A heat pump keeps a house at 21 °C while it is -10 °C outside, delivering 9 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 1100 °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 40 °C. Both engines produce the same work. Find T_m in °C.