1.Easy
A power plant delivers a net power output of 600 MW with a thermal efficiency of 50%. Find the rate Q̇L at which heat is rejected to the cooling water.
Ẇ = 600 MWη = 50%
Q̇L = MW
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 3700 kJ of heat from a hot reservoir and rejects 2960 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 3700 kJQL = 2960 kJ
W = kJ
3.Medium
A reversible (Carnot) heat engine takes in 600 kJ of heat from a reservoir at 225 °C and rejects 401 kJ per cycle. Find the temperature TL of the cold reservoir in °C.
TH = 225 °CQH = 600 kJQL = 401 kJ
TL = °C
4.Medium
A reversible refrigerator keeps a cold room at -25 °C by removing 8.5 kW of heat, and rejects heat to the surroundings at 25 °C. Find the rate Q̇H at which it rejects heat.
TL = -25 °CTH = 25 °CQ̇L = 8.5 kW
Q̇H = kW
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 700 °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 produce the same work. Find Tm in °C.
TH = 700 °CTL = 20 °C
Tm = °C
6.Hard
A heat engine takes in 4700 kJ of heat from a reservoir at 500 °C, produces 1410 kJ of work and rejects the rest to a reservoir at 35 °C, per cycle. Find the total entropy generated Sgen per cycle.
TH = 500 °CTL = 35 °CQH = 4700 kJW = 1410 kJ
Sgen = kJ/K
Answer key
- 1. Q̇L = 600 MW
- 2. W = 740 kJ
- 3. TL = 59.78 °C
- 4. Q̇H = 10.21 kW
- 5. Tm = 360 °C
- 6. Sgen = 4.598 kJ/K
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