1.Easy
A heat engine takes in 4700 kJ of heat from a hot reservoir and rejects 2585 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 4700 kJQL = 2585 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 1700 kJ of heat from a hot reservoir and rejects 1275 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 1700 kJQL = 1275 kJ
η = %
3.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 40 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 40 °CQ̇L = 8.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 225 °C and a cold reservoir at 30 °C. It takes in 4600 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 225 °CTL = 30 °CQH = 4600 kJ
Wmax = kJ
5.Hard
A heat pump keeps a house at 21 °C while it is 5 °C outside, delivering 15 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 21 °CTL = 5 °CQ̇H = 15 kW
Ẇmin = kW
6.Hard
A Carnot heat engine receives 160 kW of heat from a source at 950 °C and rejects heat to the surroundings at 27 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at -5 °C and also rejects heat to the surroundings at 27 °C. Find the rate Q̇L at which heat is removed from the freezer.
TH = 950 °CT0 = 27 °CTL = -5 °CQ̇H = 160 kW
Q̇L = kW
Answer key
- 1. W = 2115 kJ
- 2. η = 25 %
- 3. Q̇H = 10.51 kW
- 4. Wmax = 1801 kJ
- 5. Ẇmin = 0.8159 kW
- 6. Q̇L = 1012 kW
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