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 455 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 700 kJQ_L = 455 kJ

η = %

2.Easy

A heat engine takes in 2500 kJ of heat from a hot reservoir and rejects 1625 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 2500 kJQ_L = 1625 kJ

W = kJ

3.Medium

A reversible (Carnot) heat engine takes in 700 kJ of heat from a reservoir at 775 °C and rejects 222 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

T_H = 775 °CQ_H = 700 kJQ_L = 222 kJ

T_L = °C

4.Medium

A heat engine works between a hot reservoir at 250 °C and a cold reservoir at 10 °C. It takes in 1900 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 250 °CT_L = 10 °CQ_H = 1900 kJ

W_max = kJ

5.Hard

A heat pump keeps a house at 21 °C while it is 5 °C outside, delivering 4 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = 5 °CQ̇_H = 4 kW

Ẇ_min = kW

6.Hard

A refrigerator keeps its cold space at 5 °C in a kitchen at 28 °C, removing heat from the cold space at 3.5 kW. Find the minimum power input Ẇ_min.

T_H = 28 °CT_L = 5 °CQ̇_L = 3.5 kW

Ẇ_min = kW

Answer key

1. η = 35 %
2. W = 875 kJ
3. T_L = 59.26 °C
4. W_max = 871.6 kJ
5. Ẇ_min = 0.2176 kW
6. Ẇ_min = 0.2894 kW

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