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.

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Name: ____________________   Date: ____________

1.Easy
houseoutside airHPQ̇H​ = 17 kWQ̇L​Ẇ = ?

A heat pump with a coefficient of performance of 4.4 delivers 17 kW of heat to a house. Find the electrical power Ẇ it uses.

COPHP = 4.4Q̇H = 17 kW
Ẇ = kW
2.Easy
houseoutside airHPQ̇H​ = 18 kWQ̇L​ = ?Ẇ

A heat pump with a coefficient of performance of 4 delivers 18 kW of heat to a house. Find the rate Q̇L at which it takes heat from the outside air.

COPHP = 4Q̇H = 18 kW
Q̇L = kW
3.Medium
TH​ = 20 °CTL​ = 2 °CRQ̇H​ = ?Q̇L​ = 2.5 kWẆ

A reversible refrigerator keeps a cold room at 2 °C by removing 2.5 kW of heat, and rejects heat to the surroundings at 20 °C. Find the rate Q̇H at which it rejects heat.

TL = 2 °CTH = 20 °CQ̇L = 2.5 kW
Q̇H = kW
4.Medium
TH​ = 675 °CTL​ = 10 °CEQH​ = 4900 kJQL​W = ?

A heat engine works between a hot reservoir at 675 °C and a cold reservoir at 10 °C. It takes in 4900 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 675 °CTL = 10 °CQH = 4900 kJ
Wmax = kJ
5.Hard
600 °CTm​ = ?15 °CABWA​WB​

Two Carnot engines work in series. Engine A receives heat from a reservoir at 600 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 15 °C. Both engines have the same thermal efficiency. Find Tm in °C.

TH = 600 °CTL = 15 °C
Tm = °C
6.Hard
TH​ = 30 °CTL​ = -25 °CRQ̇H​Q̇L​ = 1 kWẆ = ?

A refrigerator keeps its cold space at -25 °C in a kitchen at 30 °C, removing heat from the cold space at 1 kW. Find the minimum power input Ẇmin.

TH = 30 °CTL = -25 °CQ̇L = 1 kW
Ẇmin = kW

Answer key

  1. 1. Ẇ = 3.864 kW
  2. 2. Q̇L = 13.5 kW
  3. 3. Q̇H = 2.664 kW
  4. 4. Wmax = 3437 kJ
  5. 5. Tm = 228.4 °C
  6. 6. Ẇmin = 0.2216 kW

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