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​ = 7.56 kWẆ = 2.7 kW

A refrigerator removes heat from its cold space at a rate of 7.56 kW while its compressor uses 2.7 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.

Q̇L = 7.56 kWẆ = 2.7 kW
Q̇H = kW
2.Easy
hot reservoircold reservoirEQH​ = 3900 kJQL​ = 2925 kJW = ?

A heat engine takes in 3900 kJ of heat from a hot reservoir and rejects 2925 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 3900 kJQL = 2925 kJ
W = kJ
3.Medium
TH​ = 775 °CTL​ = 35 °CEQH​QL​W

A heat engine works between a hot reservoir at 775 °C and a cold reservoir at 35 °C. Find the highest possible thermal efficiency ηmax.

TH = 775 °CTL = 35 °C
ηmax = %
4.Medium
TH​ = 200 °CTL​ = 25 °CEQH​QL​W

A heat engine works between a hot reservoir at 200 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency ηmax.

TH = 200 °CTL = 25 °C
ηmax = %
5.Hard
TH​ = 35 °CTL​ = -25 °CRQ̇H​Q̇L​ = 1.5 kWẆ = ?

A refrigerator keeps its cold space at -25 °C in a kitchen at 35 °C, removing heat from the cold space at 1.5 kW. Find the minimum power input Ẇmin.

TH = 35 °CTL = -25 °CQ̇L = 1.5 kW
Ẇmin = kW
6.Hard
TH​ = 25 °CTL​ = 5 °CRQ̇H​Q̇L​ = 2.5 kWẆ = ?

A refrigerator keeps its cold space at 5 °C in a kitchen at 25 °C, removing heat from the cold space at 2.5 kW. Find the minimum power input Ẇmin.

TH = 25 °CTL = 5 °CQ̇L = 2.5 kW
Ẇmin = kW

Answer key

  1. 1. Q̇H = 10.26 kW
  2. 2. W = 975 kJ
  3. 3. ηmax = 70.6 %
  4. 4. ηmax = 36.99 %
  5. 5. Ẇmin = 0.3627 kW
  6. 6. Ẇmin = 0.1798 kW

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