Heat engines & refrigerators worksheet with answers

Free printable Heat engines & refrigerators worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

A heat engine takes in 2100 kJ of heat from a hot reservoir and rejects 1470 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 2100 kJQ_L = 1470 kJ

η = %

2.Easy

A heat engine takes in 4600 kJ of heat from a hot reservoir and rejects 3680 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4600 kJQ_L = 3680 kJ

W = kJ

3.Medium

A reversible refrigerator keeps a cold room at -10 °C by removing 4.5 kW of heat, and rejects heat to the surroundings at 40 °C. Find the rate Q̇_H at which it rejects heat.

T_L = -10 °CT_H = 40 °CQ̇_L = 4.5 kW

Q̇_H = kW

4.Medium

A heat engine works between a hot reservoir at 800 °C and a cold reservoir at 25 °C. It takes in 4400 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 800 °CT_L = 25 °CQ_H = 4400 kJ

W_max = kJ

5.Hard

A heat engine takes in 4900 kJ of heat from a reservoir at 500 °C, produces 1813 kJ of work and rejects the rest to a reservoir at 25 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 500 °CT_L = 25 °CQ_H = 4900 kJW = 1813 kJ

S_gen = kJ/K

6.Hard

A heat pump delivers 11.5 kW of heat to a heating system at 20 °C, taking heat from a source at -5 °C. Its actual COP is 50% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

T_H = 20 °CT_L = -5 °Cη_II = 50%Q̇_H = 11.5 kW

Ẇ = kW

Answer key

1. η = 30 %
2. W = 920 kJ
3. Q̇_H = 5.355 kW
4. W_max = 3178 kJ
5. S_gen = 4.016 kJ/K
6. Ẇ = 1.961 kW

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