Parts Per Million By Volume - GE Moisture Image 1 Series Service Manual

June 2003
Parts per Million by
Volume
A-12
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:
PPM
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 is provided in nomographic form in Figure A-1 on page A-20.
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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
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 , on the Moisture Content scale.
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2. Find the expected dew/frost point for a helium gas stream having a
measured moisture content of 1000 PPM
of 0.52 atm.
Solution: In Figure A-1 on page A-20, connect 1000 PPM
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.
P
6
W
×
------- -
= 10
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P
T
and a system pressure
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Application of the Hygrometer (900-901D1)
(0-1)
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on the
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