Question:-
A moist air sample has dry bulb temperature of 30°C and specific humidity of 11.5g water vapour per kg dry air. Assume molecular weight of air as 28.93. If the saturation vapour pressure of water at 30°C is 4.24kPa and the total pressure is 90kPa, then the relative humidity (in %) of air sample is
Option (A)
50.5
Option (B)
38.5
Option(C)
56.5
Option(D)
68.5
Correct Option:
(B)
Question Solution:
Given data DBT = 30°C

w = 11.5 g/kg

Mol. Weight = 28.93

Ovs = 4.24 KPa

Pa = 90 KPa

Relative humidity = (w/0.622).(Pa/Pvs) = (11.5 / (0.622x1000)).(90 / 4.24) = 0.392 = 39.2%
question-answer-faq-2376