On a summer afternoon, the temperature was 90 F, the relative humidity was 80% a

Question

On a summer afternoon, the temperature was 90 F, the relative humidity was 80% and the barometer reading was 760 mmHg. That night, the temperature reduced to 68 F and the barometer read 760 mmHg. Calculate the percentage of water in the afternoon air that condensed to liquid water in the form of dew during the night using the PSYCHROMETRIC chart.
CHEMICAL ENGINEERING
Afternoon night time 'A' lb-mole 'B' lb-mole H2O Air H2O Air 90 F, 80% RH 68 F, 100% RH 738 mm 745 mmHg 'C' lb mole liquid water (dew)

Explanation / Answer

At condition 1; (T=90F, 738mmHg, 80% RH)
The density of water vapor in the air = 0.0017085 lb/cu.ft. of dry air

At condition2, (T=68F, 745mmHg, 100%RH)
The density of water vapor in the air = 0.00107017 lb/cu.ft. of dry air

The difference is deposited as dew = 0.00063833 lb/cu.ft.of dry air

The % deposited = (0.00063833/0.0017085) x 100 = 9%

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