1.Easy
A heat engine takes in 500 kJ of heat from a hot reservoir and rejects 275 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 500 kJQL = 275 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 3400 kJ of heat from a hot reservoir and rejects 2040 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 3400 kJQL = 2040 kJ
η = %
3.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 3.5 kW of heat, and rejects heat to the surroundings at 25 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 25 °CQ̇L = 3.5 kW
Q̇H = kW
4.Medium
A reversible (Carnot) heat engine takes in 4600 kJ of heat from a reservoir at 425 °C and rejects 2195 kJ per cycle. Find the temperature TL of the cold reservoir in °C.
TH = 425 °CQH = 4600 kJQL = 2195 kJ
TL = °C
5.Hard
A heat pump keeps a house at 22 °C while it is -10 °C outside, delivering 14 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 22 °CTL = -10 °CQ̇H = 14 kW
Ẇmin = kW
6.Hard
A refrigerator keeps its cold space at 5 °C in a kitchen at 35 °C, removing heat from the cold space at 4 kW. Find the minimum power input Ẇmin.
TH = 35 °CTL = 5 °CQ̇L = 4 kW
Ẇmin = kW
Answer key
- 1. W = 225 kJ
- 2. η = 40 %
- 3. Q̇H = 4.122 kW
- 4. TL = 59.99 °C
- 5. Ẇmin = 1.518 kW
- 6. Ẇmin = 0.4314 kW
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