Heat engines & refrigerators worksheet with answers

A power plant delivers a net power output of 300 MW with a thermal efficiency of 30%. Find the rate Q̇_L at which heat is rejected to the cooling water.

A heat engine takes in 4700 kJ of heat from a hot reservoir and rejects 2820 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

A heat engine works between a hot reservoir at 775 °C and a cold reservoir at 10 °C. It takes in 4300 kJ of heat. Find the most work W_max it could possibly produce.

A reversible refrigerator keeps a cold room at 5 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 20 °C. Find the rate Q̇_H at which it rejects heat.

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 30 °C. Both engines produce the same work. Find T_m in °C.

A heat pump delivers 15 kW of heat to a heating system at 45 °C, taking heat from a source at 10 °C. Its actual COP is 50% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.