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 3300 kJ of heat from a hot reservoir and rejects 1980 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 3300 kJQ_L = 1980 kJ

W = kJ

2.Easy

A heat engine takes in 1500 kJ of heat from a hot reservoir and rejects 1200 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 1500 kJQ_L = 1200 kJ

η = %

3.Medium

A reversible (Carnot) heat engine takes in 3400 kJ of heat from a reservoir at 300 °C and rejects 1887 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

T_H = 300 °CQ_H = 3400 kJQ_L = 1887 kJ

T_L = °C

4.Medium

A heat engine works between a hot reservoir at 725 °C and a cold reservoir at 35 °C. Find the highest possible thermal efficiency η_max.

T_H = 725 °CT_L = 35 °C

η_max = %

5.Hard

A heat pump keeps a house at 22 °C while it is 5 °C outside, delivering 6 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 22 °CT_L = 5 °CQ̇_H = 6 kW

Ẇ_min = kW

6.Hard

A refrigerator keeps its cold space at 2 °C in a kitchen at 25 °C, removing heat from the cold space at 2 kW. Find the highest possible coefficient of performance COP_max.

T_H = 25 °CT_L = 2 °CQ̇_L = 2 kW

COP_max =

Answer key

1. W = 1320 kJ
2. η = 20 %
3. T_L = 44.95 °C
4. η_max = 69.13 %
5. Ẇ_min = 0.3456 kW
6. COP_max = 11.96

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