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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1.Easy
kitchencold spaceRQ̇H​Q̇L​ = 1.8 kWẆ = 0.6 kW

A refrigerator removes heat from its cold space at a rate of 1.8 kW while its compressor uses 0.6 kW of power. Find its coefficient of performance COPR.

Q̇L = 1.8 kWẆ = 0.6 kW
COPR =
2.Easy
furnacecooling waterEQ̇H​ = ?Q̇L​Ẇ = 150 MW

A power plant delivers a net power output of 150 MW with a thermal efficiency of 35%. Find the rate of heat input Q̇H from the fuel.

Ẇ = 150 MWη = 35%
Q̇H = MW
3.Medium
TH​ = 650 °CTL​ = 40 °CEQH​ = 4100 kJQL​W = ?

A heat engine works between a hot reservoir at 650 °C and a cold reservoir at 40 °C. It takes in 4100 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 650 °CTL = 40 °CQH = 4100 kJ
Wmax = kJ
4.Medium
TH​ = 750 °CTL​ = 40 °CEQH​ = 1300 kJQL​W = ?

A heat engine works between a hot reservoir at 750 °C and a cold reservoir at 40 °C. It takes in 1300 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 750 °CTL = 40 °CQH = 1300 kJ
Wmax = kJ
5.Hard
TH​ = 22 °CTL​ = 7 °CHPQ̇H​ = 8 kWQ̇L​Ẇ = ?

A heat pump keeps a house at 22 °C while it is 7 °C outside, delivering 8 kW of heat to the house. Find the minimum power input Ẇmin.

TH = 22 °CTL = 7 °CQ̇H = 8 kW
Ẇmin = kW
6.Hard
TH​ = 25 °CTL​ = -20 °CRQ̇H​Q̇L​ = 4 kWẆ = ?

A refrigerator keeps its cold space at -20 °C in a kitchen at 25 °C, removing heat from the cold space at 4 kW. Find the minimum power input Ẇmin.

TH = 25 °CTL = -20 °CQ̇L = 4 kW
Ẇmin = kW

Answer key

  1. 1. COPR = 3
  2. 2. Q̇H = 428.6 MW
  3. 3. Wmax = 2709 kJ
  4. 4. Wmax = 902.1 kJ
  5. 5. Ẇmin = 0.4066 kW
  6. 6. Ẇmin = 0.711 kW

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