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.

New worksheet Practise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________ Date: ____________

1.Easy

A heat engine takes in 4500 kJ of heat from a hot reservoir and rejects 2475 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

Q_H = 4500 kJQ_L = 2475 kJ

η = %

2.Easy

A refrigerator removes heat from its cold space at a rate of 0.72 kW while its compressor uses 0.4 kW of power. Find its coefficient of performance COP_R.

Q̇_L = 0.72 kWẆ = 0.4 kW

COP_R =

3.Medium

A heat engine works between a hot reservoir at 575 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency η_max.

T_H = 575 °CT_L = 30 °C

η_max = %

4.Medium

A heat engine works between a hot reservoir at 250 °C and a cold reservoir at 10 °C. It takes in 2400 kJ of heat. Find the most work W_max it could possibly produce.

T_H = 250 °CT_L = 10 °CQ_H = 2400 kJ

W_max = kJ

5.Hard

Two Carnot engines work in series. Engine A receives heat from a reservoir at 800 °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 produce the same work. Find T_m in °C.

T_H = 800 °CT_L = 35 °C

T_m = °C

6.Hard

A heat engine takes in 1000 kJ of heat from a reservoir at 750 °C, produces 430 kJ of work and rejects the rest to a reservoir at 20 °C, per cycle. Find the total entropy generated S_gen per cycle.

T_H = 750 °CT_L = 20 °CQ_H = 1000 kJW = 430 kJ

S_gen = kJ/K

Answer key

1. η = 45 %
2. COP_R = 1.8
3. η_max = 64.26 %
4. W_max = 1101 kJ
5. T_m = 417.5 °C
6. S_gen = 0.967 kJ/K

Full step-by-step solutions: practise this topic on examproblems.com.