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 3760 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4700 kJQ_L = 3760 kJ

W = kJ

2.Easy

A power plant delivers a net power output of 750 MW with a thermal efficiency of 40%. Find the rate of heat input Q̇_H from the fuel.

Ẇ = 750 MWη = 40%

Q̇_H = MW

3.Medium

A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 10 °C. Find the highest possible thermal efficiency η_max.

T_H = 550 °CT_L = 10 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 350 °C and a cold reservoir at 15 °C. Find the highest possible thermal efficiency η_max.

T_H = 350 °CT_L = 15 °C

η_max = %

5.Hard

A refrigerator keeps its cold space at -10 °C in a kitchen at 25 °C, removing heat from the cold space at 5 kW. Find the minimum power input Ẇ_min.

T_H = 25 °CT_L = -10 °CQ̇_L = 5 kW

Ẇ_min = kW

6.Hard

A refrigerator keeps its cold space at -10 °C in a kitchen at 28 °C, removing heat from the cold space at 4 kW. Find the highest possible coefficient of performance COP_max.

T_H = 28 °CT_L = -10 °CQ̇_L = 4 kW

COP_max =

Answer key

1. W = 940 kJ
2. Q̇_H = 1875 MW
3. η_max = 65.6 %
4. η_max = 53.76 %
5. Ẇ_min = 0.665 kW
6. COP_max = 6.925

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