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ME 201
Thermodynamics
Second Law Practice Problems
1. Ideally, which fluid can do more work: air at 600 psia and 600°F or steam at 600
psia and 600°F
2. A heat pump provides 30,000 Btu/hr to maintain a dwelling at 68°F on a day when
the outside temperature is 35°F. The power input to the pump is 1 hp. If
electricity costs 8 cents per kilowatthour, compare the actual operating cost per
day with the minimum theoretical operating cost per day.
3. A cylinder/piston system contains water at 200 kPa, 200°C with a volume of 20
liters. The piston is moved slowly, compressing the water to a pressure of 800
kPa. The process is polytropic with a polytropic exponent of 1. Assuming that the
room temperature is 20°C, show that this process does not violate the second law.
4. When a man returns to his wellsealed house on a summer day, he finds that the
house is at 32°C. He turns on the air conditioner which cools the entire house to
20°C in 15 minutes. If the COP of the heat pump system is 2.5, determine the
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 Spring '06
 SOMERTON

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