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
furnacecooling waterEQ̇H​Q̇L​ = ?Ẇ = 1000 MW

A power plant delivers a net power output of 1000 MW with a thermal efficiency of 55%. Find the rate Q̇L at which heat is rejected to the cooling water.

Ẇ = 1000 MWη = 55%
Q̇L = MW
2.Easy
hot reservoircold reservoirEQH​ = 2000 kJQL​ = 1500 kJW = ?

A heat engine takes in 2000 kJ of heat from a hot reservoir and rejects 1500 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 2000 kJQL = 1500 kJ
W = kJ
3.Medium
TH​ = 600 °CTL​ = ?EQH​ = 3100 kJQL​ = 1023 kJW

A reversible (Carnot) heat engine takes in 3100 kJ of heat from a reservoir at 600 °C and rejects 1023 kJ per cycle. Find the temperature TL of the cold reservoir in °C.

TH = 600 °CQH = 3100 kJQL = 1023 kJ
TL = °C
4.Medium
TH​ = 28 °CTL​ = 2 °CRQ̇H​ = ?Q̇L​ = 4 kWẆ

A reversible refrigerator keeps a cold room at 2 °C by removing 4 kW of heat, and rejects heat to the surroundings at 28 °C. Find the rate Q̇H at which it rejects heat.

TL = 2 °CTH = 28 °CQ̇L = 4 kW
Q̇H = kW
5.Hard
1100 °CTm​ = ?40 °CABWA​WB​

Two Carnot engines work in series. Engine A receives heat from a reservoir at 1100 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 40 °C. Both engines have the same thermal efficiency. Find Tm in °C.

TH = 1100 °CTL = 40 °C
Tm = °C
6.Hard
TH​ = 22 °CTL​ = 5 °CHPQ̇H​ = 6 kWQ̇L​Ẇ

A heat pump keeps a house at 22 °C while it is 5 °C outside, delivering 6 kW of heat to the house. Find the highest possible coefficient of performance COPmax.

TH = 22 °CTL = 5 °CQ̇H = 6 kW
COPmax =

Answer key

  1. 1. Q̇L = 818.2 MW
  2. 2. W = 500 kJ
  3. 3. TL = 14.99 °C
  4. 4. Q̇H = 4.378 kW
  5. 5. Tm = 382.6 °C
  6. 6. COPmax = 17.36

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