Heat engines & refrigerators worksheet with answers

A heat engine takes in 1300 kJ of heat from a hot reservoir and rejects 910 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A heat engine takes in 700 kJ of heat from a hot reservoir and rejects 490 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A heat engine receives heat from a source at 650 °C and rejects heat to the surroundings at 20 °C. Its actual thermal efficiency is 51%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A heat engine receives heat from a source at 700 °C and rejects heat to the surroundings at 15 °C. Its actual thermal efficiency is 39%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A Carnot heat engine receives 190 kW of heat from a source at 850 °C and rejects heat to the surroundings at 25 °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 25 °C. Find the rate Q̇_L at which heat is removed from the freezer.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 900 °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 10 °C. Both engines have the same thermal efficiency. Find T_m in °C.