1.Easy
A heat engine takes in 2200 kJ of heat from a hot reservoir and rejects 1210 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 2200 kJQL = 1210 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 800 kJ of heat from a hot reservoir and rejects 600 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 800 kJQL = 600 kJ
W = kJ
3.Medium
A heat engine works between a hot reservoir at 700 °C and a cold reservoir at 5 °C. Find the highest possible thermal efficiency ηmax.
TH = 700 °CTL = 5 °C
ηmax = %
4.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 8 kW of heat, and rejects heat to the surroundings at 40 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 40 °CQ̇L = 8 kW
Q̇H = kW
5.Hard
A heat pump keeps a house at 21 °C while it is 7 °C outside, delivering 9 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 21 °CTL = 7 °CQ̇H = 9 kW
Ẇmin = kW
6.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 850 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 30 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 850 °CTL = 30 °C
Tm = °C
Answer key
- 1. W = 990 kJ
- 2. W = 200 kJ
- 3. ηmax = 71.42 %
- 4. Q̇H = 9.896 kW
- 5. Ẇmin = 0.4284 kW
- 6. Tm = 310.4 °C
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