1.Easy
A refrigerator removes heat from its cold space at a rate of 3.3 kW while its compressor uses 1.5 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 3.3 kWẆ = 1.5 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A heat pump with a coefficient of performance of 3.1 delivers 4 kW of heat to a house. Find the rate Q̇L at which it takes heat from the outside air.
COPHP = 3.1Q̇H = 4 kW
Q̇L = kW
3.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 8 kW of heat, and rejects heat to the surroundings at 40 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 40 °CQ̇L = 8 kW
Q̇H = kW
4.Medium
A heat engine works between a hot reservoir at 225 °C and a cold reservoir at 10 °C. Find the highest possible thermal efficiency ηmax.
TH = 225 °CTL = 10 °C
ηmax = %
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 950 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 15 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 950 °CTL = 15 °C
Tm = °C
6.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 1100 °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 have the same thermal efficiency. Find Tm in °C.
TH = 1100 °CTL = 40 °C
Tm = °C
Answer key
- 1. Q̇H = 4.8 kW
- 2. Q̇L = 2.71 kW
- 3. Q̇H = 9.896 kW
- 4. ηmax = 43.16 %
- 5. Tm = 320.5 °C
- 6. Tm = 382.6 °C
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