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 1000 kJ of heat from a hot reservoir and rejects 600 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 1000 kJQ_L = 600 kJ

η = %

2.Easy

A heat engine takes in 4200 kJ of heat from a hot reservoir and rejects 2730 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4200 kJQ_L = 2730 kJ

W = kJ

3.Medium

A heat engine works between a hot reservoir at 500 °C and a cold reservoir at 20 °C. It takes in 3900 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 500 °CT_L = 20 °CQ_H = 3900 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 275 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 275 °CT_L = 30 °C

η_max = %

5.Hard

A heat engine takes in 4700 kJ of heat from a reservoir at 850 °C, produces 2444 kJ of work and rejects the rest to a reservoir at 20 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 850 °CT_L = 20 °CQ_H = 4700 kJW = 2444 kJ

S_gen = kJ/K

6.Hard

A refrigerator keeps its cold space at -10 °C in a kitchen at 32 °C, removing heat from the cold space at 4 kW. Find the minimum power input Ẇ_min.

T_H = 32 °CT_L = -10 °CQ̇_L = 4 kW

Ẇ_min = kW

Answer key

1. η = 40 %
2. W = 1470 kJ
3. W_max = 2421 kJ
4. η_max = 44.7 %
5. S_gen = 3.511 kJ/K
6. Ẇ_min = 0.6384 kW

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