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 11.7 kW while its compressor uses 3 kW of power. Find its coefficient of performance COP_R.

Q̇_L = 11.7 kWẆ = 3 kW

COP_R =

2.Easy

A heat engine takes in 3000 kJ of heat from a hot reservoir and rejects 2100 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 3000 kJQ_L = 2100 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 300 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 300 °CT_L = 30 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 35 °C. Find the highest possible thermal efficiency η_max.

T_H = 550 °CT_L = 35 °C

η_max = %

5.Hard

A refrigerator keeps its cold space at -10 °C in a kitchen at 30 °C, removing heat from the cold space at 3 kW. Find the highest possible coefficient of performance COP_max.

T_H = 30 °CT_L = -10 °CQ̇_L = 3 kW

COP_max =

6.Hard

A refrigerator keeps its cold space at -18 °C in a kitchen at 35 °C, removing heat from the cold space at 1.5 kW. Find the minimum power input Ẇ_min.

T_H = 35 °CT_L = -18 °CQ̇_L = 1.5 kW

Ẇ_min = kW

Answer key

1. COP_R = 3.9
2. η = 30 %
3. η_max = 47.11 %
4. η_max = 62.56 %
5. COP_max = 6.579
6. Ẇ_min = 0.3116 kW

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