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​ = 3600 kJQL​ = 2700 kJW = ?

A heat engine takes in 3600 kJ of heat from a hot reservoir and rejects 2700 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 3600 kJQL = 2700 kJ
W = kJ
2.Easy
furnacecooling waterEQ̇H​ = ?Q̇L​Ẇ = 100 MW

A power plant delivers a net power output of 100 MW with a thermal efficiency of 38%. Find the rate of heat input Q̇H from the fuel.

Ẇ = 100 MWη = 38%
Q̇H = MW
3.Medium
TH​ = 250 °CTL​ = 10 °CEQH​ = 1200 kJQL​W = ?

A heat engine works between a hot reservoir at 250 °C and a cold reservoir at 10 °C. It takes in 1200 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 250 °CTL = 10 °CQH = 1200 kJ
Wmax = kJ
4.Medium
TH​ = 225 °CTL​ = 5 °CEQH​ = 3000 kJQL​W = ?

A heat engine works between a hot reservoir at 225 °C and a cold reservoir at 5 °C. It takes in 3000 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 225 °CTL = 5 °CQH = 3000 kJ
Wmax = kJ
5.Hard
TH​ = 20 °CTL​ = -10 °CHPQ̇H​ = 10 kWQ̇L​Ẇ = ?

A heat pump keeps a house at 20 °C while it is -10 °C outside, delivering 10 kW of heat to the house. Find the minimum power input Ẇmin.

TH = 20 °CTL = -10 °CQ̇H = 10 kW
Ẇmin = kW
6.Hard
TH​ = 750 °CTL​ = 15 °CEQH​ = 2900 kJQL​ = 1247 kJW = 1653 kJ

A heat engine takes in 2900 kJ of heat from a reservoir at 750 °C, produces 1653 kJ of work and rejects the rest to a reservoir at 15 °C, per cycle. Find the total entropy generated Sgen per cycle.

TH = 750 °CTL = 15 °CQH = 2900 kJW = 1653 kJ
Sgen = kJ/K

Answer key

  1. 1. W = 900 kJ
  2. 2. Q̇H = 263.2 MW
  3. 3. Wmax = 550.5 kJ
  4. 4. Wmax = 1325 kJ
  5. 5. Ẇmin = 1.023 kW
  6. 6. Sgen = 1.493 kJ/K

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