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 1700 kJ of heat from a hot reservoir and rejects 1275 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 1700 kJQ_L = 1275 kJ

W = kJ

2.Easy

A heat engine takes in 4800 kJ of heat from a hot reservoir and rejects 2640 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 4800 kJQ_L = 2640 kJ

W = kJ

3.Medium

A heat engine works between a hot reservoir at 725 °C and a cold reservoir at 10 °C. It takes in 3700 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 725 °CT_L = 10 °CQ_H = 3700 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 650 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency η_max.

T_H = 650 °CT_L = 20 °C

η_max = %

5.Hard

Two Carnot engines work in series. Engine A receives heat from a reservoir at 600 °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 25 °C. Both engines have the same thermal efficiency. Find T_m in °C.

T_H = 600 °CT_L = 25 °C

T_m = °C

6.Hard

A heat pump keeps a house at 20 °C while it is 5 °C outside, delivering 15 kW of heat to the house. Find the highest possible coefficient of performance COP_max.

T_H = 20 °CT_L = 5 °CQ̇_H = 15 kW

COP_max =

Answer key

1. W = 425 kJ
2. W = 2160 kJ
3. W_max = 2650 kJ
4. η_max = 68.24 %
5. T_m = 237.1 °C
6. COP_max = 19.54

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