1.Easy
A heat engine takes in 2300 kJ of heat from a hot reservoir and rejects 1380 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 2300 kJQL = 1380 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 1.53 kW while its compressor uses 0.9 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 1.53 kWẆ = 0.9 kW
Q̇H = kW
3.Medium
A reversible refrigerator keeps a cold room at -10 °C by removing 8 kW of heat, and rejects heat to the surroundings at 20 °C. Find the rate Q̇H at which it rejects heat.
TL = -10 °CTH = 20 °CQ̇L = 8 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 575 °C and a cold reservoir at 10 °C. It takes in 1300 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 575 °CTL = 10 °CQH = 1300 kJ
Wmax = kJ
5.Hard
A Carnot heat engine receives 160 kW of heat from a source at 600 °C and rejects heat to the surroundings at 20 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at -30 °C and also rejects heat to the surroundings at 20 °C. Find the rate Q̇L at which heat is removed from the freezer.
TH = 600 °CT0 = 20 °CTL = -30 °CQ̇H = 160 kW
Q̇L = kW
6.Hard
A heat pump keeps a house at 22 °C while it is 2 °C outside, delivering 8 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 22 °CTL = 2 °CQ̇H = 8 kW
Ẇmin = kW
Answer key
- 1. W = 920 kJ
- 2. Q̇H = 2.43 kW
- 3. Q̇H = 8.912 kW
- 4. Wmax = 866 kJ
- 5. Q̇L = 516.8 kW
- 6. Ẇmin = 0.5421 kW
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