1.Easy
A refrigerator removes heat from its cold space at a rate of 3.99 kW while its compressor uses 2.1 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 3.99 kWẆ = 2.1 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 5.92 kW while its compressor uses 1.6 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 5.92 kWẆ = 1.6 kW
Q̇H = kW
3.Medium
A heat engine works between a hot reservoir at 675 °C and a cold reservoir at 25 °C. Find the highest possible thermal efficiency ηmax.
TH = 675 °CTL = 25 °C
ηmax = %
4.Medium
A heat engine works between a hot reservoir at 350 °C and a cold reservoir at 35 °C. It takes in 1800 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 350 °CTL = 35 °CQH = 1800 kJ
Wmax = kJ
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 650 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 40 °C. Both engines produce the same work. Find Tm in °C.
TH = 650 °CTL = 40 °C
Tm = °C
6.Hard
A heat pump keeps a house at 22 °C while it is 5 °C outside, delivering 9 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 22 °CTL = 5 °CQ̇H = 9 kW
Ẇmin = kW
Answer key
- 1. Q̇H = 6.09 kW
- 2. Q̇H = 7.52 kW
- 3. ηmax = 68.55 %
- 4. Wmax = 909.9 kJ
- 5. Tm = 345 °C
- 6. Ẇmin = 0.5184 kW
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