Volumetric humidity

Volumetric humidity Y Mass of vapor per unit volume of gas-vapor mixture. It is sometimes, confusingly, called the absolute humidity, but it is really a vapor concentration preferred units are kg/m or Ib/fT, but g/nV and gr/ft are also used. It is inconvenient for calculations because it depends on temperature and pressure and on the units system absolute humidity Y is always preferAle for heat and mass balances. It is proportional to the specific humidity (wet basis) Yy = Yy/pg, where pg is the humid gas density (mass of gas-vapor mixture per unit volume, wet basis). Also... 

Table 12-1 gives formulas for conversion between absolute humidity, mole fraction, vapor pressure, and volumetric humidity for the air-water system, and Table 12-2 does likewise for a general gas-vapor system. Where relationships are not included in the definitions, they are given below. 

In U.S. units, the formulas are the same except for the volumetric humidity Y . Because of the danger of confusion with pressure units, it is recommended that in both Tables 12-1 and 12-2, Y be calculated in SI units and then converted. 

Volumetric humidity is also related to absolute humidity and humid... 

Find p if necessary by method (i) above. Find dew point from Eq. (12-4) by calculating the T corresponding to p [iteration required Antoine equation U2-5) gives a first estimate]. Calculate volumetric humidity Y , using Eq. (12-1). 

From Table 12-1, absolute humidity Y = 0.05256 kg/kg and volumetric humidity Y = 0.0492 kg/m. From the terminology section, mole fraction y = 0.0779 kmoFkmol, mole ratio z = 0.0845 kmol/kmol, specific humidity Y = 0.04994 kg/kg. 

Vapor pressure p = yP = 0.01191 x 10,000 = 119.1 Pa (0.001191 bar)—much lower than before because of the reduced total pressure. This is 0.89 mmHg. Volumetric humidity = 0.0025 kg/m —again substantially lower than at 1 atm. 

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