GE Moisture Image 1 Series, Руководство по обслуживанию, Страница: 74 / 107

June 2003
A-12 Application of the Hygrometer (900-901D1)
Parts per Million by
Volume
The water concentration in a system, in parts per million by volume,
is proportional to the ratio of the water vapor partial pressure to the
total system pressure:
(0-1)
In a closed system, increasing the total pressure of the gas will
proportionally increase the partial pressures of the various
components. The relationship between dew point, total pressure and
PPM
V
is provided in nomographic form in Figure A-1 on page A-20.
Note: The nomograph shown in Figure A-1 on page A-20 is
applicable only to gases. Do not apply it to liquids.
To compute the moisture content for any ideal gas at a given pressure,
refer to Figure A-1 on page A-20. Using a straightedge, connect the
dew point (as measured with the GE Panametrics’ Hygrometer) with
the known system pressure. Read the moisture content in PPM
V
where the straightedge crosses the moisture content scale.
Typical Problems
1. Find the water content in a nitrogen gas stream, if a dew point of -
20°C is measured and the pressure is 60 psig.
Solution : In Figure A-1 on page A-20, connect 60 psig on the
Pressure scale with -20°C on the Dew/Frost Point scale. Read 200
PPM
V
, on the Moisture Content scale.
2. Find the expected dew/frost point for a helium gas stream having a
measured moisture content of 1000 PPM
V
and a system pressure
of 0.52 atm.
Solution : In Figure A-1 on page A-20, connect 1000 PPM
V
on the
Moisture Content scale with 0.52 atm on the Pressure scale. Read
the expected frost point of
–27°C on the Dew/Frost Point scale.
PPM
V
P
W
P
T
-------- 10
6
×
=