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Unformatted text preview: ake. Assumptions 1 Both the air and water vapor are ideal gases. 2 The amount of air dissolved in water is negligible. Properties The saturation pressure of water at 15C is 1.7057 kPa (Table A4). Analysis There exists phase equilibrium at the free surface of the lake, and thus the air at the lake surface is always saturated at the interface temperature. The air at the water surface is saturated. Therefore, the partial pressure of water vapor in the air at the lake surface will simply be the saturation pressure of water at 15C, yH Lake 15C 2O,liquid side FIGURE 1624 Schematic for Example 168. Pv Psat @ 15C 1.7057 kPa The mole fraction of water vapor in the air at the surface of the lake is determined from Eq. 1622 to be yv Pv P 1.7057 kPa 92 kPa 0.0185 or 1.85 percent Water contains some dissolved air, but the amount is negligible. Therefore, we can assume the entire lake to be liquid water. Then its mole fraction becomes y water,liquid side 1.0 or 100 percent Discussion Note that the concentration of water on a molar basis is 100 percent just beneath the airwater interface and less than 2 percent just above it...
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This note was uploaded on 06/15/2009 for the course MAE 3311 taught by Professor Hajisheik during the Summer '08 term at UT Arlington.

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