Parts Per Million By Weight; Relative Humidity; Weight Of Water Per Unit Volume Of Carrier Gas - GE Moisture Image 1 Series Service Manual

Parts per Million by
Weight

Relative Humidity

Weight of Water per Unit
Volume of Carrier Gas
Application of the Hygrometer (900-901D1)
The water concentration in the gas phase of a system, in parts per
million by weight, can be calculated directly from the PPM
ratio of the molecular weight of water to that of the carrier gas as
follows:
PPM
Relative humidity is defined as the ratio of the actual water vapor
pressure to the saturation water vapor pressure at the prevailing
ambient temperature, expressed as a percentage.
RH
1. Find the relative humidity in a system, if the measured dew point
is 0°C and the ambient temperature is +20°C.
Solution: From Table A-1 on page A-20, the water vapor pressure
at a dew point of 0°C is 4.579 mm of Hg and the saturation water
vapor pressure at an ambient temperature of +20°C is 17.535 mm
of Hg. Therefore, the relative humidity of the system is
100 x 4.579/17.535 = 26.1%.
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:
mg of water
---------------------------- -
liter of gas
lb of water
------------------------- -
3
ft of gas
lb of water
------------------------------------ -
MMSCF of gas
Note: MMSCF is an abbreviation for a "million standard cubic
feet" of carrier gas.
M
W
×
--------- -
= PPM
W V
M
T
P
W
×
------- -
= 100
P
S
P
W
×
------- -
= 289
T
K
P
W
×
------- -
= 0.0324
T
R
6
×
PPM 10 P
V
= --------------- - = ---------------------- -
×
21.1 21.1
June 2003
and the
V
(0-2)
(0-3)
(0-4)
(0-5)
W
(0-6)
P
T
A-13