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 refrigerator removes heat from its cold space at a rate of 6.96 kW while its compressor uses 2.4 kW of power. Find its coefficient of performance COP_R.

Q̇_L = 6.96 kWẆ = 2.4 kW

COP_R =

2.Easy

A heat engine takes in 3200 kJ of heat from a hot reservoir and rejects 1920 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 3200 kJQ_L = 1920 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 500 °C and a cold reservoir at 35 °C. It takes in 1600 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 500 °CT_L = 35 °CQ_H = 1600 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 525 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency η_max.

T_H = 525 °CT_L = 25 °C

η_max = %

5.Hard

A heat engine takes in 2000 kJ of heat from a reservoir at 850 °C, produces 1020 kJ of work and rejects the rest to a reservoir at 25 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 850 °CT_L = 25 °CQ_H = 2000 kJW = 1020 kJ

S_gen = kJ/K

6.Hard

A heat engine takes in 500 kJ of heat from a reservoir at 900 °C, produces 190 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 = 900 °CT_L = 20 °CQ_H = 500 kJW = 190 kJ

S_gen = kJ/K

Answer key

1. COP_R = 2.9
2. η = 40 %
3. W_max = 962.3 kJ
4. η_max = 62.64 %
5. S_gen = 1.506 kJ/K
6. S_gen = 0.6313 kJ/K

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