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
hot reservoircold reservoirEQH​ = 2400 kJQL​ = 1680 kJW = ?

A heat engine takes in 2400 kJ of heat from a hot reservoir and rejects 1680 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 2400 kJQL = 1680 kJ
W = kJ
2.Easy
hot reservoircold reservoirEQH​ = 1500 kJQL​ = 975 kJW = ?

A heat engine takes in 1500 kJ of heat from a hot reservoir and rejects 975 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 1500 kJQL = 975 kJ
W = kJ
3.Medium
TH​ = 525 °CTL​ = 30 °CEQH​QL​W

A heat engine works between a hot reservoir at 525 °C and a cold reservoir at 30 °C. Find the highest possible thermal efficiency ηmax.

TH = 525 °CTL = 30 °C
ηmax = %
4.Medium
TH​ = 775 °CTL​ = ?EQH​ = 2600 kJQL​ = 690 kJW

A reversible (Carnot) heat engine takes in 2600 kJ of heat from a reservoir at 775 °C and rejects 690 kJ per cycle. Find the temperature TL of the cold reservoir in °C.

TH = 775 °CQH = 2600 kJQL = 690 kJ
TL = °C
5.Hard
TH​ = 20 °CTL​ = -10 °CHPQ̇H​ = 5 kWQ̇L​Ẇ

A heat pump keeps a house at 20 °C while it is -10 °C outside, delivering 5 kW of heat to the house. Find the highest possible coefficient of performance COPmax.

TH = 20 °CTL = -10 °CQ̇H = 5 kW
COPmax =
6.Hard
TH​ = 22 °CTL​ = 2 °CHPQ̇H​ = 5 kWQ̇L​Ẇ

A heat pump keeps a house at 22 °C while it is 2 °C outside, delivering 5 kW of heat to the house. Find the highest possible coefficient of performance COPmax.

TH = 22 °CTL = 2 °CQ̇H = 5 kW
COPmax =

Answer key

  1. 1. W = 720 kJ
  2. 2. W = 525 kJ
  3. 3. ηmax = 62.02 %
  4. 4. TL = 5.013 °C
  5. 5. COPmax = 9.772
  6. 6. COPmax = 14.76

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