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
houseoutside airHPQ̇H​ = 10.5 kWQ̇L​Ẇ = ?

A heat pump with a coefficient of performance of 3.6 delivers 10.5 kW of heat to a house. Find the electrical power Ẇ it uses.

COPHP = 3.6Q̇H = 10.5 kW
Ẇ = kW
2.Easy
hot reservoircold reservoirEQH​ = 1300 kJQL​ = 1040 kJW = ?

A heat engine takes in 1300 kJ of heat from a hot reservoir and rejects 1040 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 1300 kJQL = 1040 kJ
W = kJ
3.Medium
TH​ = 200 °CTL​ = 35 °CEQH​ = 4600 kJQL​W = ?

A heat engine works between a hot reservoir at 200 °C and a cold reservoir at 35 °C. It takes in 4600 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 200 °CTL = 35 °CQH = 4600 kJ
Wmax = kJ
4.Medium
TH​ = 750 °CTL​ = 20 °CEQH​QL​W

A heat engine works between a hot reservoir at 750 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency ηmax.

TH = 750 °CTL = 20 °C
ηmax = %
5.Hard
TH​ = 22 °CTL​ = 7 °CHPQ̇H​ = 13 kWQ̇L​Ẇ = ?

A heat pump keeps a house at 22 °C while it is 7 °C outside, delivering 13 kW of heat to the house. Find the minimum power input Ẇmin.

TH = 22 °CTL = 7 °CQ̇H = 13 kW
Ẇmin = kW
6.Hard
1050 °CTm​ = ?25 °CABWA​WB​

Two Carnot engines work in series. Engine A receives heat from a reservoir at 1050 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 25 °C. Both engines have the same thermal efficiency. Find Tm in °C.

TH = 1050 °CTL = 25 °C
Tm = °C

Answer key

  1. 1. Ẇ = 2.917 kW
  2. 2. W = 260 kJ
  3. 3. Wmax = 1604 kJ
  4. 4. ηmax = 71.35 %
  5. 5. Ẇmin = 0.6607 kW
  6. 6. Tm = 354.9 °C

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