1.Easy
A heat engine takes in 1100 kJ of heat from a hot reservoir and rejects 605 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 1100 kJQL = 605 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 3200 kJ of heat from a hot reservoir and rejects 2240 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 3200 kJQL = 2240 kJ
W = kJ
3.Medium
A reversible refrigerator keeps a cold room at -30 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 35 °C. Find the rate Q̇H at which it rejects heat.
TL = -30 °CTH = 35 °CQ̇L = 8.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 700 °C and a cold reservoir at 20 °C. It takes in 2800 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 700 °CTL = 20 °CQH = 2800 kJ
Wmax = kJ
5.Hard
A refrigerator keeps its cold space at 2 °C in a kitchen at 35 °C, removing heat from the cold space at 2.5 kW. Find the minimum power input Ẇmin.
TH = 35 °CTL = 2 °CQ̇L = 2.5 kW
Ẇmin = kW
6.Hard
A heat pump keeps a house at 20 °C while it is -10 °C outside, delivering 11 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 20 °CTL = -10 °CQ̇H = 11 kW
Ẇmin = kW
Answer key
- 1. W = 495 kJ
- 2. W = 960 kJ
- 3. Q̇H = 10.77 kW
- 4. Wmax = 1957 kJ
- 5. Ẇmin = 0.2998 kW
- 6. Ẇmin = 1.126 kW
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