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 2300 kJ of heat from a hot reservoir and rejects 1725 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 2300 kJQ_L = 1725 kJ

W = kJ

2.Easy

A heat engine takes in 2200 kJ of heat from a hot reservoir and rejects 1320 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 2200 kJQ_L = 1320 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency η_max.

T_H = 550 °CT_L = 20 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 500 °C and a cold reservoir at 10 °C. Find the highest possible thermal efficiency η_max.

T_H = 500 °CT_L = 10 °C

η_max = %

5.Hard

A refrigerator keeps its cold space at 4 °C in a kitchen at 30 °C, removing heat from the cold space at 4.5 kW. Find the minimum power input Ẇ_min.

T_H = 30 °CT_L = 4 °CQ̇_L = 4.5 kW

Ẇ_min = kW

6.Hard

A refrigerator keeps its cold space at -20 °C in a kitchen at 28 °C, removing heat from the cold space at 3.5 kW. Find the minimum power input Ẇ_min.

T_H = 28 °CT_L = -20 °CQ̇_L = 3.5 kW

Ẇ_min = kW

Answer key

1. W = 575 kJ
2. η = 40 %
3. η_max = 64.39 %
4. η_max = 63.38 %
5. Ẇ_min = 0.4222 kW
6. Ẇ_min = 0.6636 kW

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