1.Easy
A heat engine takes in 4300 kJ of heat from a hot reservoir and rejects 2580 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 4300 kJQL = 2580 kJ
η = %
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 3280 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 4100 kJQL = 3280 kJ
η = %
3.Medium
A reversible refrigerator keeps a cold room at 5 °C by removing 6.5 kW of heat, and rejects heat to the surroundings at 20 °C. Find the rate Q̇H at which it rejects heat.
TL = 5 °CTH = 20 °CQ̇L = 6.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 750 °C and a cold reservoir at 40 °C. Find the highest possible thermal efficiency ηmax.
TH = 750 °CTL = 40 °C
ηmax = %
5.Hard
A Carnot heat engine receives 20 kW of heat from a source at 650 °C and rejects heat to the surroundings at 20 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at 0 °C and also rejects heat to the surroundings at 20 °C. Find the rate Q̇L at which heat is removed from the freezer.
TH = 650 °CT0 = 20 °CTL = 0 °CQ̇H = 20 kW
Q̇L = kW
6.Hard
A refrigerator keeps its cold space at -20 °C in a kitchen at 32 °C, removing heat from the cold space at 3.5 kW. Find the minimum power input Ẇmin.
TH = 32 °CTL = -20 °CQ̇L = 3.5 kW
Ẇmin = kW
Answer key
- 1. η = 40 %
- 2. η = 20 %
- 3. Q̇H = 6.851 kW
- 4. ηmax = 69.39 %
- 5. Q̇L = 186.4 kW
- 6. Ẇmin = 0.7189 kW
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