1.Easy
A refrigerator removes heat from its cold space at a rate of 1.61 kW while its compressor uses 0.7 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 1.61 kWẆ = 0.7 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 4100 kJ of heat from a hot reservoir and rejects 3280 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 4100 kJQL = 3280 kJ
η = %
3.Medium
A heat engine works between a hot reservoir at 525 °C and a cold reservoir at 25 °C. It takes in 3100 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 525 °CTL = 25 °CQH = 3100 kJ
Wmax = kJ
4.Medium
A reversible refrigerator keeps a cold room at -25 °C by removing 7 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = -25 °CTH = 30 °CQ̇L = 7 kW
Q̇H = kW
5.Hard
A heat pump keeps a house at 22 °C while it is 7 °C outside, delivering 7 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 22 °CTL = 7 °CQ̇H = 7 kW
Ẇmin = kW
6.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 600 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 15 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 600 °CTL = 15 °C
Tm = °C
Answer key
- 1. Q̇H = 2.31 kW
- 2. η = 20 %
- 3. Wmax = 1942 kJ
- 4. Q̇H = 8.551 kW
- 5. Ẇmin = 0.3558 kW
- 6. Tm = 228.4 °C
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