1.Easy
A heat engine takes in 3000 kJ of heat from a hot reservoir and rejects 1650 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 3000 kJQL = 1650 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 7.74 kW while its compressor uses 1.8 kW of power. Find its coefficient of performance COPR.
Q̇L = 7.74 kWẆ = 1.8 kW
COPR =
3.Medium
A reversible (Carnot) heat engine takes in 2000 kJ of heat from a reservoir at 375 °C and rejects 920 kJ per cycle. Find the temperature TL of the cold reservoir in °C.
TH = 375 °CQH = 2000 kJQL = 920 kJ
TL = °C
4.Medium
A reversible refrigerator keeps a cold room at -10 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 28 °C. Find the rate Q̇H at which it rejects heat.
TL = -10 °CTH = 28 °CQ̇L = 8.5 kW
Q̇H = kW
5.Hard
A heat pump keeps a house at 20 °C while it is 0 °C outside, delivering 8 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 20 °CTL = 0 °CQ̇H = 8 kW
Ẇmin = kW
6.Hard
A refrigerator keeps its cold space at 2 °C in a kitchen at 25 °C, removing heat from the cold space at 4.5 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = 2 °CQ̇L = 4.5 kW
Ẇmin = kW
Answer key
- 1. W = 1350 kJ
- 2. COPR = 4.3
- 3. TL = 25 °C
- 4. Q̇H = 9.727 kW
- 5. Ẇmin = 0.5458 kW
- 6. Ẇmin = 0.3762 kW
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