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 4900 kJ of heat from a hot reservoir and rejects 3430 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4900 kJQ_L = 3430 kJ

η = %

2.Easy

A heat engine takes in 3400 kJ of heat from a hot reservoir and rejects 2720 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 3400 kJQ_L = 2720 kJ

W = kJ

3.Medium

A heat engine works between a hot reservoir at 325 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 325 °CT_L = 30 °C

η_max = %

4.Medium

A reversible (Carnot) heat engine takes in 1800 kJ of heat from a reservoir at 300 °C and rejects 858 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

T_H = 300 °CQ_H = 1800 kJQ_L = 858 kJ

T_L = °C

5.Hard

A refrigerator keeps its cold space at -18 °C in a kitchen at 35 °C, removing heat from the cold space at 5 kW. Find the minimum power input Ẇ_min.

T_H = 35 °CT_L = -18 °CQ̇_L = 5 kW

Ẇ_min = kW

6.Hard

A heat pump keeps a house at 22 °C while it is 0 °C outside, delivering 5 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 22 °CT_L = 0 °CQ̇_H = 5 kW

Ẇ_min = kW

Answer key

1. η = 30 %
2. W = 680 kJ
3. η_max = 49.32 %
4. T_L = 0.0515 °C
5. Ẇ_min = 1.039 kW
6. Ẇ_min = 0.3727 kW

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