Saturday, April 01, 2006
HW #2 - P #8 - Relative Humidity
A thermos bottle is half-filled with water and is left open to the atmospheric air at 70°F and 35% relative humidity. If heat transfer to the water through the thermos walls and the free surface is negligible, determine the temperature of water when phase equilibrium is established.
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3 comments:
again like #7 can you assume that the atmospheric pressure exerted on the liquid is 1 atm?
Anon @ 4:50
You can assume Patm = 1 atm or 101.325 kPa, but it is not necessary to solve the problem.
Determine the Twater that would give a vapor pressure that is equal to the partial pressure of the water in the air far from the bottle (hr = 35%,Tair=70 degF).
graham @ 2:29
Yes, pahse equilibrium here is when hr = 100%.
The key here is that although the air STAYS at 70 degF, the Twater drops. This is caused by the evaporation of the water. The water does not stay at 70 degF because the bottle is insulated.
This means that the partial pressure of the water in the air far from the bottle and the vapor pressure of the water @ Twater (unknown) must be the same. The goal is to determine the Twater at which phase equilibrium occurs.
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