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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Name: ____________________ Date: ____________

1.Easy

A heat pump with a coefficient of performance of 4.4 delivers 9 kW of heat to a house. Find the electrical power Ẇ it uses.

COP_HP = 4.4Q̇_H = 9 kW

Ẇ = kW

2.Easy

A heat engine takes in 3000 kJ of heat from a hot reservoir and rejects 1800 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 3000 kJQ_L = 1800 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency η_max.

T_H = 550 °CT_L = 25 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 400 °C and a cold reservoir at 30 °C. It takes in 600 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 400 °CT_L = 30 °CQ_H = 600 kJ

W_max = kJ

5.Hard

A refrigerator keeps its cold space at -18 °C in a kitchen at 30 °C, removing heat from the cold space at 1.5 kW. Find the minimum power input Ẇ_min.

T_H = 30 °CT_L = -18 °CQ̇_L = 1.5 kW

Ẇ_min = kW

6.Hard

A heat pump keeps a house at 20 °C while it is -5 °C outside, delivering 7 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 20 °CT_L = -5 °CQ̇_H = 7 kW

Ẇ_min = kW

Answer key

1. Ẇ = 2.045 kW
2. η = 40 %
3. η_max = 63.78 %
4. W_max = 329.8 kJ
5. Ẇ_min = 0.2822 kW
6. Ẇ_min = 0.597 kW

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