1.Easy
A heat engine takes in 2900 kJ of heat from a hot reservoir and rejects 2175 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 2900 kJQL = 2175 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 3.78 kW while its compressor uses 2.1 kW of power. Find its coefficient of performance COPR.
Q̇L = 3.78 kWẆ = 2.1 kW
COPR =
3.Medium
A reversible refrigerator keeps a cold room at 0 °C by removing 0.5 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = 0 °CTH = 30 °CQ̇L = 0.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 650 °C and a cold reservoir at 40 °C. Find the highest possible thermal efficiency ηmax.
TH = 650 °CTL = 40 °C
ηmax = %
5.Hard
A refrigerator keeps its cold space at -10 °C in a kitchen at 25 °C, removing heat from the cold space at 1 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = -10 °CQ̇L = 1 kW
Ẇmin = kW
6.Hard
A heat engine takes in 900 kJ of heat from a reservoir at 750 °C, produces 441 kJ of work and rejects the rest to a reservoir at 35 °C, per cycle. Find the total entropy generated Sgen per cycle.
TH = 750 °CTL = 35 °CQH = 900 kJW = 441 kJ
Sgen = kJ/K
Answer key
- 1. W = 725 kJ
- 2. COPR = 1.8
- 3. Q̇H = 0.5549 kW
- 4. ηmax = 66.08 %
- 5. Ẇmin = 0.133 kW
- 6. Sgen = 0.6099 kJ/K
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