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 power plant delivers a net power output of 400 MW with a thermal efficiency of 40%. Find the rate of heat input Q̇_H from the fuel.

Ẇ = 400 MWη = 40%

Q̇_H = MW

2.Easy

A heat pump with a coefficient of performance of 3.8 delivers 18 kW of heat to a house. Find the electrical power Ẇ it uses.

COP_HP = 3.8Q̇_H = 18 kW

Ẇ = kW

3.Medium

A heat engine works between a hot reservoir at 375 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 375 °CT_L = 30 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 600 °C and a cold reservoir at 35 °C. It takes in 1700 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 600 °CT_L = 35 °CQ_H = 1700 kJ

W_max = kJ

5.Hard

A heat pump keeps a house at 21 °C while it is -5 °C outside, delivering 7 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = -5 °CQ̇_H = 7 kW

Ẇ_min = kW

6.Hard

A refrigerator keeps its cold space at 5 °C in a kitchen at 32 °C, removing heat from the cold space at 4 kW. Find the highest possible coefficient of performance COP_max.

T_H = 32 °CT_L = 5 °CQ̇_L = 4 kW

COP_max =

Answer key

1. Q̇_H = 1000 MW
2. Ẇ = 4.737 kW
3. η_max = 53.23 %
4. W_max = 1100 kJ
5. Ẇ_min = 0.6187 kW
6. COP_max = 10.3

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