Heat engines & refrigerators worksheet with answers

A heat engine takes in 4700 kJ of heat from a hot reservoir and rejects 3525 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

A power plant delivers a net power output of 750 MW with a thermal efficiency of 33%. Find the rate of heat input Q̇_H from the fuel.

A heat engine works between a hot reservoir at 775 °C and a cold reservoir at 15 °C. It takes in 1700 kJ of heat. Find the most work W_max it could possibly produce.

A heat engine receives heat from a source at 600 °C and rejects heat to the surroundings at 20 °C. Its actual thermal efficiency is 40%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 500 °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 produce the same work. Find T_m in °C.

A heat pump delivers 12 kW of heat to a heating system at 45 °C, taking heat from a source at -5 °C. Its actual COP is 30% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.