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# Units of Measure (Flow of Air and GHe through a valve)

## Units of Measure (Flow of Air and GHe through a valve)

(OP)
I have Delta P vs. Flow Rate data for air flowing through a particular valve.  The unit of measure for the flow rate is scfm.  Now, I know that scfm is the mass flow rate divided by the density of the fluid at standard atmospheric conditions.  The problem is that I want to flow He through the valve instead of air.  How can I relate the test data of this valve to my conditions?  Is it a simple ratio of the densities of the fluids?  If so, is that at standard atmospheric conditions or at test conditions?  Thanks.

### RE: Units of Measure (Flow of Air and GHe through a valve)

Hinspate:

I don't quite understand your question, but perhaps this will help.

1 lb-mol of any gas is equivalent to 379.48 scf (standard cubic feet) of that gas.  In other words, dry air has a molecular weight of 28.85 and so 28.85 lbs of dry air is equal to 379.48 scf at standard conditions of 60 deg F and 1 atmosphere pressure. Similarly, helium has a molecular weight of 4.00, so 4.00 lbs of helium is also equal to 379.48 scf at 60 deg F and 1 atmosphere.

In metric units, 1 kg-mol of any gas is equivalent to 22.41 Nm3 (normal cubic meters) of that gas.  So, 28.85 kg of dry air is equal to 22.41 Nm3 at normal conditions of 0 deg C and 1 atmosphere.  Similarly, 4.00 kg of helium is also equal to 22.41 Nm3 at 0 deg C and 1 atmosphere.

Note the change between the standard conditions of temperature and pressure in the USA units and the normal conditions of temperature and pressure in the metric units.  Also note the metric system uses "normal conditions" and the USA system uses "standard conditions".

Milton Beychok
mbeychok@home.com
Air Pollution Dispersion Modeling
Visit my website to learn about "Fundamentals of Stack Gas Dispersion", a most comprehensive book on dispersion modeling of continuous, buoyant air pollution plumes. The site has published peer reviews and the complete Table of Contents.

### RE: Units of Measure (Flow of Air and GHe through a valve)

check with the manufacturer first, they might be able to give you the
calibration data you need.

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