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 refrigerator removes heat from its cold space at a rate of 3.85 kW while its compressor uses 1.1 kW of power. Find its coefficient of performance COP_R.

Q̇_L = 3.85 kWẆ = 1.1 kW

COP_R =

2.Easy

A heat engine takes in 3200 kJ of heat from a hot reservoir and rejects 2240 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 3200 kJQ_L = 2240 kJ

W = kJ

3.Medium

A heat engine works between a hot reservoir at 800 °C and a cold reservoir at 40 °C. Find the highest possible thermal efficiency η_max.

T_H = 800 °CT_L = 40 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 475 °C and a cold reservoir at 15 °C. Find the highest possible thermal efficiency η_max.

T_H = 475 °CT_L = 15 °C

η_max = %

5.Hard

A heat pump keeps a house at 22 °C while it is 7 °C outside, delivering 12 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 22 °CT_L = 7 °CQ̇_H = 12 kW

Ẇ_min = kW

6.Hard

A heat pump keeps a house at 22 °C while it is -10 °C outside, delivering 6 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 22 °CT_L = -10 °CQ̇_H = 6 kW

Ẇ_min = kW

Answer key

1. COP_R = 3.5
2. W = 960 kJ
3. η_max = 70.82 %
4. η_max = 61.48 %
5. Ẇ_min = 0.6099 kW
6. Ẇ_min = 0.6505 kW

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