Heat engines & refrigerators worksheet with answers

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 takes in 800 kJ of heat from a hot reservoir and rejects 480 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A reversible refrigerator keeps a cold room at -25 °C by removing 6 kW of heat, and rejects heat to the surroundings at 40 °C. Find the rate Q̇_H at which it rejects heat.

A reversible (Carnot) heat engine takes in 3400 kJ of heat from a reservoir at 475 °C and rejects 1446 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

A Carnot heat engine receives 100 kW of heat from a source at 400 °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.

Two Carnot engines work in series. Engine A receives heat from a reservoir at 600 °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 30 °C. Both engines produce the same work. Find T_m in °C.