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 4700 kJ of heat from a hot reservoir and rejects 3760 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4700 kJQ_L = 3760 kJ

η = %

2.Easy

A heat engine takes in 3600 kJ of heat from a hot reservoir and rejects 2340 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 3600 kJQ_L = 2340 kJ

η = %

3.Medium

A heat engine works between a hot reservoir at 625 °C and a cold reservoir at 20 °C. It takes in 1200 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 625 °CT_L = 20 °CQ_H = 1200 kJ

W_max = kJ

4.Medium

A heat engine works between a hot reservoir at 700 °C and a cold reservoir at 5 °C. Find the highest possible thermal efficiency η_max.

T_H = 700 °CT_L = 5 °C

η_max = %

5.Hard

A heat engine takes in 3300 kJ of heat from a reservoir at 750 °C, produces 1848 kJ of work and rejects the rest to a reservoir at 30 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 750 °CT_L = 30 °CQ_H = 3300 kJW = 1848 kJ

S_gen = kJ/K

6.Hard

Two Carnot engines work in series. Engine A receives heat from a reservoir at 650 °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 35 °C. Both engines have the same thermal efficiency. Find T_m in °C.

T_H = 650 °CT_L = 35 °C

T_m = °C

Answer key

1. η = 20 %
2. η = 35 %
3. W_max = 808.3 kJ
4. η_max = 71.42 %
5. S_gen = 1.564 kJ/K
6. T_m = 260.2 °C

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