1.Easy
A refrigerator removes heat from its cold space at a rate of 9.36 kW while its compressor uses 2.4 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 9.36 kWẆ = 2.4 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 2900 kJ of heat from a hot reservoir and rejects 1740 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 2900 kJQL = 1740 kJ
η = %
3.Medium
A reversible refrigerator keeps a cold room at -5 °C by removing 0.5 kW of heat, and rejects heat to the surroundings at 20 °C. Find the rate Q̇H at which it rejects heat.
TL = -5 °CTH = 20 °CQ̇L = 0.5 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 600 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency ηmax.
TH = 600 °CTL = 25 °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 2 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = -10 °CQ̇L = 2 kW
Ẇmin = kW
6.Hard
A refrigerator keeps its cold space at -25 °C in a kitchen at 35 °C, removing heat from the cold space at 4 kW. Find the highest possible coefficient of performance COPmax.
TH = 35 °CTL = -25 °CQ̇L = 4 kW
COPmax =
Answer key
- 1. Q̇H = 11.76 kW
- 2. η = 40 %
- 3. Q̇H = 0.5466 kW
- 4. ηmax = 65.85 %
- 5. Ẇmin = 0.266 kW
- 6. COPmax = 4.136
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