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​ = 3200 kJQL​ = 2240 kJW = ?

A heat engine takes in 3200 kJ of heat from a hot reservoir and rejects 2240 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 3200 kJQL = 2240 kJ
W = kJ
2.Easy
hot reservoircold reservoirEQH​ = 1600 kJQL​ = 1200 kJW = ?

A heat engine takes in 1600 kJ of heat from a hot reservoir and rejects 1200 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 1600 kJQL = 1200 kJ
W = kJ
3.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 = %
4.Medium
TH​ = 550 °CTL​ = 10 °CEQH​ = 4900 kJQL​W = ?

A heat engine works between a hot reservoir at 550 °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 = 550 °CTL = 10 °CQH = 4900 kJ
Wmax = kJ
5.Hard
TH​ = 30 °CTL​ = -18 °CRQ̇H​Q̇L​ = 5 kWẆ

A refrigerator keeps its cold space at -18 °C in a kitchen at 30 °C, removing heat from the cold space at 5 kW. Find the highest possible coefficient of performance COPmax.

TH = 30 °CTL = -18 °CQ̇L = 5 kW
COPmax =
6.Hard
TH​ = 22 °CTL​ = 5 °CHPQ̇H​ = 11.5 kWQ̇L​Ẇ = ?

A heat pump delivers 11.5 kW of heat to a heating system at 22 °C, taking heat from a source at 5 °C. Its actual COP is 55% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.

TH = 22 °CTL = 5 °CηII = 55%Q̇H = 11.5 kW
Ẇ = kW

Answer key

  1. 1. W = 960 kJ
  2. 2. W = 400 kJ
  3. 3. ηmax = 36.99 %
  4. 4. Wmax = 3214 kJ
  5. 5. COPmax = 5.316
  6. 6. Ẇ = 1.204 kW

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