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 500 kJ of heat from a hot reservoir and rejects 300 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 500 kJQ_L = 300 kJ

η = %

2.Easy

A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 3075 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4100 kJQ_L = 3075 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 275 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency η_max.

T_H = 275 °CT_L = 25 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 450 °C and a cold reservoir at 25 °C. It takes in 4700 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 450 °CT_L = 25 °CQ_H = 4700 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 highest possible coefficient of performance COP_max.

T_H = 21 °CT_L = -10 °CQ̇_H = 5 kW

COP_max =

6.Hard

A heat pump delivers 18 kW of heat to a heating system at 22 °C, taking heat from a source at -10 °C. Its actual COP is 40% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

T_H = 22 °CT_L = -10 °Cη_II = 40%Q̇_H = 18 kW

Ẇ = kW

Answer key

1. η = 40 %
2. η = 25 %
3. η_max = 45.61 %
4. W_max = 2762 kJ
5. COP_max = 9.489
6. Ẇ = 4.879 kW

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