A moist air sample has dry bulb temperature of 30°C and

A moist air sample has dry bulb temperature of 30°C and specific humidity of 11.5 g 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 4.24 kPa and the total pressure is 90 kPa, then the relative humidity (in%) of air sample is

Given: DBT = 30°C, w = 11.5 g/kg
∴ Relative humidity

=	Specific humidity	×	Total pressure
	0.622		saturation vapour pressure

φ =	w	×	P_a
	0.622		P_vs

φ =	11.5 × 90	= 0.385
	0.622 × 1000 × 4.24

φ ≈ 38.5%