Heat engines & refrigerators worksheet with answers

A heat engine takes in 2000 kJ of heat from a hot reservoir and rejects 1300 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

A refrigerator removes heat from its cold space at a rate of 0.46 kW while its compressor uses 0.2 kW of power. Find its coefficient of performance COP_R.

A heat engine works between a hot reservoir at 225 °C and a cold reservoir at 25 °C. It takes in 1400 kJ of heat. Find the most work W_max it could possibly produce.

A heat engine receives heat from a source at 450 °C and rejects heat to the surroundings at 25 °C. Its actual thermal efficiency is 35%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

A Carnot heat engine receives 140 kW of heat from a source at 950 °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 -20 °C and also rejects heat to the surroundings at 25 °C. Find the rate Q̇_L at which heat is removed from the freezer.

A heat pump delivers 18.5 kW of heat to a heating system at 21 °C, taking heat from a source at 0 °C. Its actual COP is 50% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.