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 4400 kJ of heat from a hot reservoir and rejects 2860 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4400 kJQ_L = 2860 kJ

W = kJ

2.Easy

A heat engine takes in 1600 kJ of heat from a hot reservoir and rejects 1120 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 1600 kJQ_L = 1120 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 500 °C and a cold reservoir at 35 °C. It takes in 3400 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 500 °CT_L = 35 °CQ_H = 3400 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 400 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 400 °CT_L = 30 °C

η_max = %

5.Hard

A heat pump keeps a house at 20 °C while it is 0 °C outside, delivering 6 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 20 °CT_L = 0 °CQ̇_H = 6 kW

Ẇ_min = kW

6.Hard

Two Carnot engines work in series. Engine A receives heat from a reservoir at 900 °C and rejects heat to an intermediate reservoir at temperature T_m. Engine B takes all that heat and rejects heat to a reservoir at 30 °C. Both engines have the same thermal efficiency. Find T_m in °C.

T_H = 900 °CT_L = 30 °C

T_m = °C

Answer key

1. W = 1540 kJ
2. η = 30 %
3. W_max = 2045 kJ
4. η_max = 54.97 %
5. Ẇ_min = 0.4093 kW
6. T_m = 323.2 °C

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