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 1155 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 2100 kJQ_L = 1155 kJ

η = %

2.Easy

A heat engine takes in 4300 kJ of heat from a hot reservoir and rejects 2795 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4300 kJQ_L = 2795 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 625 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency η_max.

T_H = 625 °CT_L = 20 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 650 °C and a cold reservoir at 40 °C. It takes in 4700 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 650 °CT_L = 40 °CQ_H = 4700 kJ

W_max = kJ

5.Hard

A refrigerator keeps its cold space at -25 °C in a kitchen at 32 °C, removing heat from the cold space at 3.5 kW. Find the minimum power input Ẇ_min.

T_H = 32 °CT_L = -25 °CQ̇_L = 3.5 kW

Ẇ_min = kW

6.Hard

A heat pump keeps a house at 21 °C while it is 2 °C outside, delivering 5 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = 2 °CQ̇_H = 5 kW

Ẇ_min = kW

Answer key

1. η = 45 %
2. η = 35 %
3. η_max = 67.36 %
4. W_max = 3106 kJ
5. Ẇ_min = 0.8039 kW
6. Ẇ_min = 0.323 kW

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