4/9/98
A-16
Application of the Hygrometer (900-901D1)
Weight of Water per Unit Volume of Carrier Gas
Three units of measure are commonly used in the gas industry to
express the weight of water per unit volume of carrier gas. They
all represent a vapor density and are derivable from the vapor
pressure of water and the Perfect Gas Laws. Referenced to a
temperature of 60°F and a pressure of 14.7 psia, the following
equations may be used to calculate these units:
(4)
(5)
(6)
Note:
MMSCF is an abbreviation for a “million standard cubic
feet” of carrier gas.
Weight of Water per Unit Weight of Carrier Gas
Occasionally, the moisture content of a gas is expressed in terms
of the weight of water per unit weight of carrier gas. In such a
case, the unit of measure defined by the following equation is the
most commonly used:
(7)
For ambient air at 1 atm of pressure, the above equation reduces
to the following:
(8)
mg of water
liter of gas
-----------------------------
289
P
W
T
K
--------
×
=
lb of water
ft
3
of gas
--------------------------
0.0324
P
W
T
R
--------
×
=
lb of water
MMSCF of gas
-------------------------------------
PPM
V
21.1
----------------
10
6
P
W
×
21.1
P
T
×
-----------------------
=
=
grains of water
lb of gas
------------------------------------
7000
M
W
P
W
×
M
T
P
T
×
------------------------
×
=
grains of water
lb of gas
------------------------------------
5.72
P
W
×
=
