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 3400 kJ of heat from a hot reservoir and rejects 2210 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 3400 kJQ_L = 2210 kJ

W = kJ

2.Easy

A heat engine takes in 800 kJ of heat from a hot reservoir and rejects 560 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 800 kJQ_L = 560 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 375 °C and a cold reservoir at 40 °C. It takes in 5000 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 375 °CT_L = 40 °CQ_H = 5000 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 725 °C and a cold reservoir at 30 °C. It takes in 1300 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 725 °CT_L = 30 °CQ_H = 1300 kJ

W_max = kJ

5.Hard

A refrigerator keeps its cold space at -18 °C in a kitchen at 25 °C, removing heat from the cold space at 2 kW. Find the minimum power input Ẇ_min.

T_H = 25 °CT_L = -18 °CQ̇_L = 2 kW

Ẇ_min = kW

6.Hard

A heat engine takes in 1100 kJ of heat from a reservoir at 500 °C, produces 473 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 = 500 °CT_L = 20 °CQ_H = 1100 kJW = 473 kJ

S_gen = kJ/K

Answer key

1. W = 1190 kJ
2. η = 30 %
3. W_max = 2584 kJ
4. W_max = 905.2 kJ
5. Ẇ_min = 0.3371 kW
6. S_gen = 0.7161 kJ/K

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