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​ = 2000 kJQL​ = 1300 kJW = ?

A heat engine takes in 2000 kJ of heat from a hot reservoir and rejects 1300 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 2000 kJQL = 1300 kJ
W = kJ
2.Easy
hot reservoircold reservoirEQH​ = 3100 kJQL​ = 2170 kJW = ?

A heat engine takes in 3100 kJ of heat from a hot reservoir and rejects 2170 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 3100 kJQL = 2170 kJ
W = kJ
3.Medium
TH​ = 350 °CTL​ = ?EQH​ = 2200 kJQL​ = 1035 kJW

A reversible (Carnot) heat engine takes in 2200 kJ of heat from a reservoir at 350 °C and rejects 1035 kJ per cycle. Find the temperature TL of the cold reservoir in °C.

TH = 350 °CQH = 2200 kJQL = 1035 kJ
TL = °C
4.Medium
TH​ = 250 °CTL​ = 40 °CEQH​ = 4900 kJQL​W = ?

A heat engine works between a hot reservoir at 250 °C and a cold reservoir at 40 °C. It takes in 4900 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 250 °CTL = 40 °CQH = 4900 kJ
Wmax = kJ
5.Hard
TH​ = 30 °CTL​ = -20 °CRQ̇H​Q̇L​ = 2 kWẆ = ?

A refrigerator keeps its cold space at -20 °C in a kitchen at 30 °C, removing heat from the cold space at 2 kW. Find the minimum power input Ẇmin.

TH = 30 °CTL = -20 °CQ̇L = 2 kW
Ẇmin = kW
6.Hard
TH​ = 30 °CTL​ = 2 °CRQ̇H​Q̇L​ = 5 kWẆ

A refrigerator keeps its cold space at 2 °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 = 2 °CQ̇L = 5 kW
COPmax =

Answer key

  1. 1. W = 700 kJ
  2. 2. W = 930 kJ
  3. 3. TL = 20.01 °C
  4. 4. Wmax = 1967 kJ
  5. 5. Ẇmin = 0.395 kW
  6. 6. COPmax = 9.827

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