Heat engines & refrigerators worksheet with answers

A heat pump with a coefficient of performance of 4.3 delivers 12.5 kW of heat to a house. Find the rate Q̇_L at which it takes heat from the outside air.

A heat engine takes in 1400 kJ of heat from a hot reservoir and rejects 1050 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 500 °C and a cold reservoir at 40 °C. It takes in 1400 kJ of heat. Find the most work W_max it could possibly produce.

A heat engine works between a hot reservoir at 575 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency η_max.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 550 °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 35 °C. Both engines produce the same work. Find T_m in °C.

A Carnot heat engine receives 30 kW of heat from a source at 750 °C and rejects heat to the surroundings at 20 °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 20 °C. Find the rate Q̇_L at which heat is removed from the freezer.