1.Easy
A heat engine takes in 3400 kJ of heat from a hot reservoir and rejects 2720 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 3400 kJQL = 2720 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 500 kJ of heat from a hot reservoir and rejects 350 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 500 kJQL = 350 kJ
W = kJ
3.Medium
A heat engine receives heat from a source at 700 °C and rejects heat to the surroundings at 40 °C. Its actual thermal efficiency is 41%. Find its second-law efficiency ηII, the ratio of the actual efficiency to the Carnot efficiency.
TH = 700 °CTL = 40 °Cη = 41%
ηII = %
4.Medium
A reversible refrigerator keeps a cold room at -5 °C by removing 7 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 = 7 kW
Q̇H = kW
5.Hard
A refrigerator keeps its cold space at -18 °C in a kitchen at 25 °C, removing heat from the cold space at 2.5 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = -18 °CQ̇L = 2.5 kW
Ẇmin = kW
6.Hard
A refrigerator keeps its cold space at 2 °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 = 2 °CQ̇L = 3.5 kW
Ẇmin = kW
Answer key
- 1. W = 680 kJ
- 2. W = 150 kJ
- 3. ηII = 60.45 %
- 4. Q̇H = 7.653 kW
- 5. Ẇmin = 0.4213 kW
- 6. Ẇmin = 0.3816 kW
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