Humid Air : Relative air humidity

Air psychrometrics

1. Introduction

The relative humidity is defined as ratio of the partial pressure of water in the air over the saturation pressure of water at the dry bulb temperature of the considered humid air.

2. Calculation

ε = Pwater / Pwatersat
With :
ε = Relative humidify of air (-)
Pwater = Partial pressure of water (Pa)
Pwatersat = saturation pressure of water at the dry bulb temperature of the humid air (Pa)

3. Use

The relative air humidity is often used in dry bulk handling where a relative humidity of 45-50% at max 25c is normally a good practice to reduce the risk of caking of the materials.