1.Easy
A refrigerator removes heat from its cold space at a rate of 3.3 kW while its compressor uses 1 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 3.3 kWẆ = 1 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 4400 kJ of heat from a hot reservoir and rejects 3520 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 4400 kJQL = 3520 kJ
W = kJ
3.Medium
A heat engine works between a hot reservoir at 350 °C and a cold reservoir at 40 °C. Find the highest possible thermal efficiency ηmax.
TH = 350 °CTL = 40 °C
ηmax = %
4.Medium
A reversible refrigerator keeps a cold room at -30 °C by removing 5.5 kW of heat, and rejects heat to the surroundings at 25 °C. Find the rate Q̇H at which it rejects heat.
TL = -30 °CTH = 25 °CQ̇L = 5.5 kW
Q̇H = kW
5.Hard
A heat pump delivers 9 kW of heat to a heating system at 45 °C, taking heat from a source at -5 °C. Its actual COP is 60% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.
TH = 45 °CTL = -5 °CηII = 60%Q̇H = 9 kW
Ẇ = kW
6.Hard
A heat pump keeps a house at 22 °C while it is 2 °C outside, delivering 11 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 22 °CTL = 2 °CQ̇H = 11 kW
Ẇmin = kW
Answer key
- 1. Q̇H = 4.3 kW
- 2. W = 880 kJ
- 3. ηmax = 49.75 %
- 4. Q̇H = 6.744 kW
- 5. Ẇ = 2.357 kW
- 6. Ẇmin = 0.7454 kW
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