Solutions to Selected Chapter Problems

Let x = weight fraction of vapor. Then, from a material balance, solve forx  

3 From steam tables, Ph20 90°F = 36.1 mm Hg. Determine partial pressure of H20 vapor in air. 

The dew point is the temperature at which the water vapor in the air begins to condense. This would occur at the vapor pressure of 11.16 mm Hg, or about 55°F. 

Note that the correct value (measured) is 42.3°C for this vapor pressure. Linear interpolation would have given an incorrect value of 37.7°C. 

Component B is a stagnant gas in the column, hence Ngz is 0 throughout the column. 

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