Moist Air - Mole Fraction of Water Vapor
Mole fraction of water vapor is the ratio of water molecules to air and water molecules.
The mole fraction of water vapor is the ratio of the number of mole of water vapor in the moist air - to the total number of mole of dry air and water vapor.
The mole fraction of water vapor in moist air can be expressed as
xw = nw / (na + nw) (1)
where
xw = mole fraction of water vapor
nw = mole of water
na = mole of air