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​ = 17 kWQ̇L​ = ?Ẇ

A heat pump with a coefficient of performance of 4.6 delivers 17 kW of heat to a house. Find the rate Q̇L at which it takes heat from the outside air.

COPHP = 4.6Q̇H = 17 kW
Q̇L = kW
2.Easy
hot reservoircold reservoirEQH​ = 900 kJQL​ = 630 kJW = ?

A heat engine takes in 900 kJ of heat from a hot reservoir and rejects 630 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 900 kJQL = 630 kJ
W = kJ
3.Medium
TH​ = 25 °CTL​ = -25 °CRQ̇H​ = ?Q̇L​ = 3 kWẆ

A reversible refrigerator keeps a cold room at -25 °C by removing 3 kW of heat, and rejects heat to the surroundings at 25 °C. Find the rate Q̇H at which it rejects heat.

TL = -25 °CTH = 25 °CQ̇L = 3 kW
Q̇H = kW
4.Medium
TH​ = 675 °CTL​ = 15 °CEQH​ = 3900 kJQL​W = ?

A heat engine works between a hot reservoir at 675 °C and a cold reservoir at 15 °C. It takes in 3900 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 675 °CTL = 15 °CQH = 3900 kJ
Wmax = kJ
5.Hard
TH​ = 45 °CTL​ = 10 °CHPQ̇H​ = 12.5 kWQ̇L​Ẇ = ?

A heat pump delivers 12.5 kW of heat to a heating system at 45 °C, taking heat from a source at 10 °C. Its actual COP is 30% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

TH = 45 °CTL = 10 °CηII = 30%Q̇H = 12.5 kW
Ẇ = kW
6.Hard
TH​ = 21 °CTL​ = 7 °CHPQ̇H​ = 6 kWQ̇L​Ẇ

A heat pump keeps a house at 21 °C while it is 7 °C outside, delivering 6 kW of heat to the house. Find the highest possible coefficient of performance COPmax.

TH = 21 °CTL = 7 °CQ̇H = 6 kW
COPmax =

Answer key

  1. 1. Q̇L = 13.3 kW
  2. 2. W = 270 kJ
  3. 3. Q̇H = 3.604 kW
  4. 4. Wmax = 2715 kJ
  5. 5. Ẇ = 4.584 kW
  6. 6. COPmax = 21.01

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