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 4700 kJ of heat from a hot reservoir and rejects 3290 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4700 kJQ_L = 3290 kJ

η = %

2.Easy

A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 3280 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4100 kJQ_L = 3280 kJ

W = kJ

3.Medium

A heat engine receives heat from a source at 400 °C and rejects heat to the surroundings at 15 °C. Its actual thermal efficiency is 34%. Find its second-law efficiency η_II, the ratio of the actual efficiency to the Carnot efficiency.

T_H = 400 °CT_L = 15 °Cη = 34%

η_II = %

4.Medium

A heat engine works between a hot reservoir at 425 °C and a cold reservoir at 10 °C. Find the highest possible thermal efficiency η_max.

T_H = 425 °CT_L = 10 °C

η_max = %

5.Hard

A heat engine takes in 1600 kJ of heat from a reservoir at 450 °C, produces 448 kJ of work and rejects the rest to a reservoir at 40 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 450 °CT_L = 40 °CQ_H = 1600 kJW = 448 kJ

S_gen = kJ/K

6.Hard

A refrigerator keeps its cold space at 5 °C in a kitchen at 25 °C, removing heat from the cold space at 1.5 kW. Find the highest possible coefficient of performance COP_max.

T_H = 25 °CT_L = 5 °CQ̇_L = 1.5 kW

COP_max =

Answer key

1. η = 30 %
2. W = 820 kJ
3. η_II = 59.45 %
4. η_max = 59.44 %
5. S_gen = 1.466 kJ/K
6. COP_max = 13.91

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