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 worksheetPractise 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
kitchencold spaceRQ̇H​Q̇L​ = 1.92 kWẆ = 0.8 kW

A refrigerator removes heat from its cold space at a rate of 1.92 kW while its compressor uses 0.8 kW of power. Find its coefficient of performance COPR.

Q̇L = 1.92 kWẆ = 0.8 kW
COPR =
2.Easy
hot reservoircold reservoirEQH​ = 4700 kJQL​ = 3760 kJW

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.

QH = 4700 kJQL = 3760 kJ
η = %
3.Medium
TH​ = 375 °CTL​ = 5 °CEQH​QL​W

A heat engine works between a hot reservoir at 375 °C and a cold reservoir at 5 °C. Find the highest possible thermal efficiency ηmax.

TH = 375 °CTL = 5 °C
ηmax = %
4.Medium
TH​ = 375 °CTL​ = 20 °CEQH​ = 4800 kJQL​W = ?

A heat engine works between a hot reservoir at 375 °C and a cold reservoir at 20 °C. It takes in 4800 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 375 °CTL = 20 °CQH = 4800 kJ
Wmax = kJ
5.Hard
TH​ = 35 °CTL​ = 5 °CHPQ̇H​ = 5 kWQ̇L​Ẇ = ?

A heat pump delivers 5 kW of heat to a heating system at 35 °C, taking heat from a source at 5 °C. Its actual COP is 60% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

TH = 35 °CTL = 5 °CηII = 60%Q̇H = 5 kW
Ẇ = kW
6.Hard
TH​ = 22 °CTL​ = 2 °CHPQ̇H​ = 6 kWQ̇L​Ẇ = ?

A heat pump keeps a house at 22 °C while it is 2 °C outside, delivering 6 kW of heat to the house. Find the minimum power input Ẇmin.

TH = 22 °CTL = 2 °CQ̇H = 6 kW
Ẇmin = kW

Answer key

  1. 1. COPR = 2.4
  2. 2. η = 20 %
  3. 3. ηmax = 57.09 %
  4. 4. Wmax = 2629 kJ
  5. 5. Ẇ = 0.8113 kW
  6. 6. Ẇmin = 0.4066 kW

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