1.Easy
A heat engine takes in 4800 kJ of heat from a hot reservoir and rejects 3840 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 4800 kJQL = 3840 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 5000 kJ of heat from a hot reservoir and rejects 3000 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 5000 kJQL = 3000 kJ
W = kJ
3.Medium
A reversible refrigerator keeps a cold room at -10 °C by removing 9 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = -10 °CTH = 30 °CQ̇L = 9 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 350 °C and a cold reservoir at 30 °C. It takes in 4000 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 350 °CTL = 30 °CQH = 4000 kJ
Wmax = kJ
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 750 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 20 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 750 °CTL = 20 °C
Tm = °C
6.Hard
A refrigerator keeps its cold space at -25 °C in a kitchen at 28 °C, removing heat from the cold space at 1 kW. Find the minimum power input Ẇmin.
TH = 28 °CTL = -25 °CQ̇L = 1 kW
Ẇmin = kW
Answer key
- 1. W = 960 kJ
- 2. W = 2000 kJ
- 3. Q̇H = 10.37 kW
- 4. Wmax = 2054 kJ
- 5. Tm = 274.5 °C
- 6. Ẇmin = 0.2136 kW
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