Page 100 - Industrial Ventilation Design Guidebook

4,2 STATE VALUES OF HUMID AIR; MOLLIER DIAGRAMS AND THEIR APPLICATIONS 65

TABLE 4.5 Minor Constituents of Dry Air

Parts per million

Gas Symbol Molecular weight Volume Weight

Neon. Ne 20.183 18 12.9
Helium He 4.003 5.2 0.74
Methane CH 4 16.04 2.2 1.3
Krypton Kr 83.8 1 3
Nitrous oxide N 2 O 44.01 1 1.6
Hydrogen 2.016 0.5 0.03
H 2
Xenon Xe 131.3 0.08 0.37
Ozone 0 3 48.00 0.01 0.02
Radon Rn 222 0.06 x 10~ u —

The molar mass of dry air is dependent on the consistency of air, but for stan-
dard air it is M i = 0.028964 kg/mol. In practical calculations we may use the rough
value of 0.0290 kg/mol. The molar mass of water vapor is M h = 0.0180153 kg/mol
and the rough value used in practical calculations is 0.0180 kg/mol.
According to the state equation of ideal gas, the partial density of dry air
in humid air is

where p i is the partial pressure of dry air and R is the gas constant. According
to present knowledge, the best value for the gas constant is

In practical calculations we use the value of R = 8.314 J/mol K.
The partial density of water vapor in humid air is

where p h is the partial pressure of water vapor.
The density of humid air is the sum of the partial densities of dry air and
water vaoor.

and the total pressure of humid air is a sum of the partial pressures of dry air and
water vapor:

The mass of dry air in a volume V is denoted as m r (p i = w^/V,) and the
mass of water vapor in V is m h (p h — m h/V h). Humidity of air, meaning the
ratio of water vapor mass to dry air mass, is defined as