1.Easy
A heat engine takes in 1100 kJ of heat from a hot reservoir and rejects 770 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 1100 kJQL = 770 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A power plant delivers a net power output of 200 MW with a thermal efficiency of 55%. Find the rate of heat input Q̇H from the fuel.
Ẇ = 200 MWη = 55%
Q̇H = MW
3.Medium
A heat engine works between a hot reservoir at 725 °C and a cold reservoir at 5 °C. Find the highest possible thermal efficiency ηmax.
TH = 725 °CTL = 5 °C
ηmax = %
4.Medium
A reversible refrigerator keeps a cold room at 2 °C by removing 2 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = 2 °CTH = 30 °CQ̇L = 2 kW
Q̇H = kW
5.Hard
A refrigerator keeps its cold space at -20 °C in a kitchen at 32 °C, removing heat from the cold space at 3 kW. Find the minimum power input Ẇmin.
TH = 32 °CTL = -20 °CQ̇L = 3 kW
Ẇmin = kW
6.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 1100 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 35 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 1100 °CTL = 35 °C
Tm = °C
Answer key
- 1. W = 330 kJ
- 2. Q̇H = 363.6 MW
- 3. ηmax = 72.13 %
- 4. Q̇H = 2.204 kW
- 5. Ẇmin = 0.6162 kW
- 6. Tm = 377.3 °C
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