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​ = 3500 kJQL​ = 2800 kJW

A heat engine takes in 3500 kJ of heat from a hot reservoir and rejects 2800 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.

QH = 3500 kJQL = 2800 kJ
η = %
2.Easy
houseoutside airHPQ̇H​ = 16.5 kWQ̇L​ = ?Ẇ

A heat pump with a coefficient of performance of 2.5 delivers 16.5 kW of heat to a house. Find the rate Q̇L at which it takes heat from the outside air.

COPHP = 2.5Q̇H = 16.5 kW
Q̇L = kW
3.Medium
TH​ = 225 °CTL​ = ?EQH​ = 800 kJQL​ = 487 kJW

A reversible (Carnot) heat engine takes in 800 kJ of heat from a reservoir at 225 °C and rejects 487 kJ per cycle. Find the temperature TL of the cold reservoir in °C.

TH = 225 °CQH = 800 kJQL = 487 kJ
TL = °C
4.Medium
TH​ = 550 °CTL​ = 25 °CEQH​ = 1600 kJQL​W = ?

A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 25 °C. It takes in 1600 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 550 °CTL = 25 °CQH = 1600 kJ
Wmax = kJ
5.Hard
TH​ = 35 °CTL​ = -18 °CRQ̇H​Q̇L​ = 3 kWẆ = ?

A refrigerator keeps its cold space at -18 °C in a kitchen at 35 °C, removing heat from the cold space at 3 kW. Find the minimum power input Ẇmin.

TH = 35 °CTL = -18 °CQ̇L = 3 kW
Ẇmin = kW
6.Hard
TH​ = 21 °CTL​ = 5 °CHPQ̇H​ = 17 kWQ̇L​Ẇ = ?

A heat pump delivers 17 kW of heat to a heating system at 21 °C, taking heat from a source at 5 °C. Its actual COP is 30% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

TH = 21 °CTL = 5 °CηII = 30%Q̇H = 17 kW
Ẇ = kW

Answer key

  1. 1. η = 20 %
  2. 2. Q̇L = 9.9 kW
  3. 3. TL = 30.1 °C
  4. 4. Wmax = 1020 kJ
  5. 5. Ẇmin = 0.6232 kW
  6. 6. Ẇ = 3.082 kW

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