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​ = 2560 kJW = ?

A heat engine takes in 3200 kJ of heat from a hot reservoir and rejects 2560 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.

QH = 3200 kJQL = 2560 kJ
W = kJ
2.Easy
houseoutside airHPQ̇H​ = 13.5 kWQ̇L​Ẇ = ?

A heat pump with a coefficient of performance of 2.9 delivers 13.5 kW of heat to a house. Find the electrical power Ẇ it uses.

COPHP = 2.9Q̇H = 13.5 kW
Ẇ = kW
3.Medium
TH​ = 625 °CTL​ = 20 °CEQH​QL​W

A heat engine works between a hot reservoir at 625 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency ηmax.

TH = 625 °CTL = 20 °C
ηmax = %
4.Medium
TH​ = 650 °CTL​ = 20 °CEQH​ = 1400 kJQL​W = ?

A heat engine works between a hot reservoir at 650 °C and a cold reservoir at 20 °C. It takes in 1400 kJ of heat. Find the most work Wmax it could possibly produce.

TH = 650 °CTL = 20 °CQH = 1400 kJ
Wmax = kJ
5.Hard
750 °CTm​ = ?15 °CABWA​WB​

Two Carnot engines work in series. Engine A receives heat from a reservoir at 750 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 15 °C. Both engines produce the same work. Find Tm in °C.

TH = 750 °CTL = 15 °C
Tm = °C
6.Hard
TH​ = 30 °CTL​ = 2 °CRQ̇H​Q̇L​ = 2.5 kWẆ

A refrigerator keeps its cold space at 2 °C in a kitchen at 30 °C, removing heat from the cold space at 2.5 kW. Find the highest possible coefficient of performance COPmax.

TH = 30 °CTL = 2 °CQ̇L = 2.5 kW
COPmax =

Answer key

  1. 1. W = 640 kJ
  2. 2. Ẇ = 4.655 kW
  3. 3. ηmax = 67.36 %
  4. 4. Wmax = 955.4 kJ
  5. 5. Tm = 382.5 °C
  6. 6. COPmax = 9.827

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