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 4400 kJ of heat from a hot reservoir and rejects 2860 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4400 kJQ_L = 2860 kJ

η = %

2.Easy

A heat engine takes in 2800 kJ of heat from a hot reservoir and rejects 1680 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 2800 kJQ_L = 1680 kJ

W = kJ

3.Medium

A reversible (Carnot) heat engine takes in 4700 kJ of heat from a reservoir at 750 °C and rejects 1416 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

T_H = 750 °CQ_H = 4700 kJQ_L = 1416 kJ

T_L = °C

4.Medium

A heat engine works between a hot reservoir at 600 °C and a cold reservoir at 35 °C. It takes in 1600 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 600 °CT_L = 35 °CQ_H = 1600 kJ

W_max = kJ

5.Hard

A heat pump keeps a house at 21 °C while it is -10 °C outside, delivering 5 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = -10 °CQ̇_H = 5 kW

Ẇ_min = kW

6.Hard

A heat pump delivers 16 kW of heat to a heating system at 20 °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.

T_H = 20 °CT_L = -5 °Cη_II = 30%Q̇_H = 16 kW

Ẇ = kW

Answer key

1. η = 35 %
2. W = 1120 kJ
3. T_L = 35.1 °C
4. W_max = 1035 kJ
5. Ẇ_min = 0.5269 kW
6. Ẇ = 4.548 kW

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