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 700 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 = 700 kJQ_L = 560 kJ

η = %

2.Easy

A power plant delivers a net power output of 500 MW with a thermal efficiency of 40%. Find the rate Q̇_L at which heat is rejected to the cooling water.

Ẇ = 500 MWη = 40%

Q̇_L = MW

3.Medium

A heat engine works between a hot reservoir at 575 °C and a cold reservoir at 30 °C. It takes in 700 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 575 °CT_L = 30 °CQ_H = 700 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 475 °C and a cold reservoir at 35 °C. Find the highest possible thermal efficiency η_max.

T_H = 475 °CT_L = 35 °C

η_max = %

5.Hard

A heat pump keeps a house at 20 °C while it is 0 °C outside, delivering 7 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 20 °CT_L = 0 °CQ̇_H = 7 kW

Ẇ_min = kW

6.Hard

A heat pump keeps a house at 21 °C while it is 0 °C outside, delivering 12 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = 0 °CQ̇_H = 12 kW

Ẇ_min = kW

Answer key

1. η = 20 %
2. Q̇_L = 750 MW
3. W_max = 449.8 kJ
4. η_max = 58.81 %
5. Ẇ_min = 0.4776 kW
6. Ẇ_min = 0.8567 kW

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