Chapter 14 MASS TRANSFER
Chapter 14 MASS TRANSFER
Chapter 14 MASS TRANSFER
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<strong>Chapter</strong> <strong>14</strong> Mass Transfer<strong>14</strong>-35 The mole fraction of the water vapor at the surface of a lake at a specified temperature is to bedetermined.Assumptions 1 Both the air and water vapor are ideal gases. 2 Air at the lake surface is saturated.Properties The saturation pressure of water at 15C is 1.705 kPa (Table A-9).Analysis The air at the water surface will be saturated.Therefore, the partial pressure of water vapor in the airat the lake surface will simply be the saturation pressureof water at 15C,Pvapor Psat@15 C 1705 . kPaSaturated air13.8 psiay H2O, air sideAssuming both the air and vapor to be ideal gases, thepartial pressure and mole fraction of dry air in the air atthe surface of the lake are determined to beP P P 100 1705 . 98.295dry air vapor kPaLake, 60ºFy H2O, liquid side = 1.0ydry airPdry air 98.295kPa 0.983P 100 kPa(or 98.3%)Therefore, the mole fraction of dry air is 98.3 percent just above the air-water interface.<strong>14</strong>-12
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