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
hot reservoircold reservoirEQH​ = 4100 kJQL​ = 2870 kJW = ?

A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 2870 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 4100 kJQL = 2870 kJ
W = kJ
2.Easy
hot reservoircold reservoirEQH​ = 4100 kJQL​ = 3280 kJW = ?

A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 3280 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 4100 kJQL = 3280 kJ
W = kJ
3.Medium
TH​ = 275 °CTL​ = 30 °CEQH​QL​W

A heat engine works between a hot reservoir at 275 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency ηmax.

TH = 275 °CTL = 30 °C
ηmax = %
4.Medium
TH​ = 450 °CTL​ = ?EQH​ = 1300 kJQL​ = 500 kJW

A reversible (Carnot) heat engine takes in 1300 kJ of heat from a reservoir at 450 °C and rejects 500 kJ per cycle. Find the temperature TL of the cold reservoir in °C.

TH = 450 °CQH = 1300 kJQL = 500 kJ
TL = °C
5.Hard
TH​ = 28 °CTL​ = 2 °CRQ̇H​Q̇L​ = 4.5 kWẆ = ?

A refrigerator keeps its cold space at 2 °C in a kitchen at 28 °C, removing heat from the cold space at 4.5 kW. Find the minimum power input Ẇmin.

TH = 28 °CTL = 2 °CQ̇L = 4.5 kW
Ẇmin = kW
6.Hard
TH​ = 35 °CTL​ = -20 °CRQ̇H​Q̇L​ = 1 kWẆ = ?

A refrigerator keeps its cold space at -20 °C in a kitchen at 35 °C, removing heat from the cold space at 1 kW. Find the minimum power input Ẇmin.

TH = 35 °CTL = -20 °CQ̇L = 1 kW
Ẇmin = kW

Answer key

  1. 1. W = 1230 kJ
  2. 2. W = 820 kJ
  3. 3. ηmax = 44.7 %
  4. 4. TL = 4.985 °C
  5. 5. Ẇmin = 0.4252 kW
  6. 6. Ẇmin = 0.2173 kW

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