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 3100 kJ of heat from a hot reservoir and rejects 2015 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 3100 kJQ_L = 2015 kJ

η = %

2.Easy

A heat engine takes in 1800 kJ of heat from a hot reservoir and rejects 990 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

Q_H = 1800 kJQ_L = 990 kJ

W = kJ

3.Medium

A reversible (Carnot) heat engine takes in 900 kJ of heat from a reservoir at 575 °C and rejects 338 kJ per cycle. Find the temperature T_L of the cold reservoir in °C.

T_H = 575 °CQ_H = 900 kJQ_L = 338 kJ

T_L = °C

4.Medium

A heat engine works between a hot reservoir at 575 °C and a cold reservoir at 40 °C. It takes in 1300 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 575 °CT_L = 40 °CQ_H = 1300 kJ

W_max = kJ

5.Hard

A heat engine takes in 2400 kJ of heat from a reservoir at 900 °C, produces 1416 kJ of work and rejects the rest to a reservoir at 40 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 900 °CT_L = 40 °CQ_H = 2400 kJW = 1416 kJ

S_gen = kJ/K

6.Hard

A heat pump keeps a house at 21 °C while it is 5 °C outside, delivering 7 kW of heat to the house. Find the minimum power input Ẇ_min.

T_H = 21 °CT_L = 5 °CQ̇_H = 7 kW

Ẇ_min = kW

Answer key

1. η = 35 %
2. W = 810 kJ
3. T_L = 45.38 °C
4. W_max = 820 kJ
5. S_gen = 1.096 kJ/K
6. Ẇ_min = 0.3808 kW

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