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 1500 kJ of heat from a hot reservoir and rejects 900 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 1500 kJQ_L = 900 kJ

η = %

2.Easy

A heat engine takes in 3600 kJ of heat from a hot reservoir and rejects 2340 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 3600 kJQ_L = 2340 kJ

W = kJ

3.Medium

A heat engine works between a hot reservoir at 625 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 625 °CT_L = 30 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 450 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency η_max.

T_H = 450 °CT_L = 20 °C

η_max = %

5.Hard

A heat pump delivers 12 kW of heat to a heating system at 22 °C, taking heat from a source at -10 °C. Its actual COP is 30% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

T_H = 22 °CT_L = -10 °Cη_II = 30%Q̇_H = 12 kW

Ẇ = kW

6.Hard

A refrigerator keeps its cold space at -18 °C in a kitchen at 35 °C, removing heat from the cold space at 5 kW. Find the minimum power input Ẇ_min.

T_H = 35 °CT_L = -18 °CQ̇_L = 5 kW

Ẇ_min = kW

Answer key

1. η = 40 %
2. W = 1260 kJ
3. η_max = 66.25 %
4. η_max = 59.46 %
5. Ẇ = 4.337 kW
6. Ẇ_min = 1.039 kW

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