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 1400 kJ of heat from a hot reservoir and rejects 910 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 1400 kJQ_L = 910 kJ

η = %

2.Easy

A heat engine takes in 4400 kJ of heat from a hot reservoir and rejects 2640 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4400 kJQ_L = 2640 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 600 °C and a cold reservoir at 25 °C. It takes in 2400 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 600 °CT_L = 25 °CQ_H = 2400 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 450 °C and a cold reservoir at 35 °C. It takes in 3600 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 450 °CT_L = 35 °CQ_H = 3600 kJ

W_max = kJ

5.Hard

A refrigerator keeps its cold space at 5 °C in a kitchen at 32 °C, removing heat from the cold space at 2.5 kW. Find the highest possible coefficient of performance COP_max.

T_H = 32 °CT_L = 5 °CQ̇_L = 2.5 kW

COP_max =

6.Hard

A heat pump keeps a house at 20 °C while it is 7 °C outside, delivering 6 kW of heat to the house. Find the highest possible coefficient of performance COP_max.

T_H = 20 °CT_L = 7 °CQ̇_H = 6 kW

COP_max =

Answer key

1. η = 35 %
2. η = 40 %
3. W_max = 1580 kJ
4. W_max = 2066 kJ
5. COP_max = 10.3
6. COP_max = 22.55

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