1.Easy
A heat engine takes in 3600 kJ of heat from a hot reservoir and rejects 2340 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 3600 kJQL = 2340 kJ
η = %
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 4900 kJ of heat from a hot reservoir and rejects 3675 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 4900 kJQL = 3675 kJ
W = kJ
3.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 9.5 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 30 °CQ̇L = 9.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 200 °C and a cold reservoir at 15 °C. It takes in 2600 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 200 °CTL = 15 °CQH = 2600 kJ
Wmax = kJ
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 1200 °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 produce the same work. Find Tm in °C.
TH = 1200 °CTL = 35 °C
Tm = °C
6.Hard
A refrigerator keeps its cold space at -20 °C in a kitchen at 35 °C, removing heat from the cold space at 3.5 kW. Find the minimum power input Ẇmin.
TH = 35 °CTL = -20 °CQ̇L = 3.5 kW
Ẇmin = kW
Answer key
- 1. η = 35 %
- 2. W = 1225 kJ
- 3. Q̇H = 11.38 kW
- 4. Wmax = 1017 kJ
- 5. Tm = 617.5 °C
- 6. Ẇmin = 0.7604 kW
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