how do you find the density of humid air?

Answer 1

"The density of moist air may be determined by a similar relation: D = 1.2929 (273.13/T) [(B - 0.3783e)/760] where T is the absolute temperature; B, the barometric pressure in mm, and e the vapor pressure of the moisture in the air in mm." From the first reference.

It might be easier to use the relative humidity, temperature and atmospheric pressure values in the moist air calculator at the site below:

Answer 2

ρ = 1 / v = (p / Ra T) (1 + x) / (1 + x Rw / Ra) (3)

v = specific volume of moist air per mass unit of dry air and water vapor (m3/kg)

Ra = 286.9 - the individual gas constant air (J/kg.K)

Rw = 461.5 - the individual gas constant water vapor (J/kg.K)

x = specific humidity or humidity ratio (kg/kg)

p = pressure in the humid air (Pa)

Answer 3

You look it up in the CRC handbook of Chemistry and Physics. This big book is in most libraries.