cm^3/s to ppmV 1

[ajdowdell]

Ok, so I work at a facility building valves. I'm being asked to meet differing fugitie emission standards. there are 3 that I know of, and I'm trying to get a handle units of measurement. I think this has been sorta hashed out before on here, but the thread was closed.

The 3 standards I'm looking at are:

1. ISO 15848-1 (Type testing) very in depth requires heat cycling, 6 bar, casing around the packing, data acquisition, 500 strokes or even 1000 for CO2 service, requires measurement of ALL helium that leaks past the entire stem diameter (ppmV) or a sniffer test that reads in ppmV. there also some other options

2. ISO 15848-2 (production testing) also requires that the device read in ppmV

3. Shell Spec MESC SPE 77/312 requires high pressures, qualified technicians and units to be atm*cm^3/s

 

[ajdowdell]

GOOD, GOOD, GOOD! I like it when a plan comes together, and everyone is on the same page!

Its good to see these as well, I will double check just to make sure...

1 ppmV = 1 ml/m3 = 0.176 mg/m3 = 0.136 mg/kg = 0.136 ppmM

1 ppmM = 1 mg/kg = 1.29 mg/m3 = 7.32 ml/m3 = 7.32 ppmV

Thanks for all your help!

 

[ajdowdell]

"In the case of Helium in air, for example: 1 ppmV = 1 ml/m3 = 0.176 mg/m3 = 0.136 mg/kg = 0.136 ppmM 1 ppmM = 1 mg/kg = 1.29 mg/m3 = 7.32 ml/m3 = 7.32 ppmV(please double-check against other sources, if you like...)"

I haven't found any sources yet, but does this assume atmospheric pressure? I'm thinking that helium volume will compress at a different rate (volume/pressure) than will the rest of "air" correct?

That would mean that if you had a different air pressure (high altitude vs low altitude or indoor HVAC either pressurized building or vacc building depending on building vintage compared to outdoor testing-- for examples) the actual volumetric concentration would change, while since by definition mass must be conserved, would not change. So ppm (mass) will remain constant, while ppmv would technically very with air pressure.

Maybe this affect isn't noticable when dealing with these smaller pressure changes, but when dealing with such small concentrations maybe it does...

 

[btrueblood]

Generally, the valve (with helium in it) will be at a high enough pressure relative to ambient, that the small variation due to atmposheric conditions can be safely ignored. I.e. the leak rate of helium won't vary by much.

As far as the volume/volume comparison, I believe this gets normalized by the actual vacuum conditions achieved inside the ion chamber.

In reality, you will have much more variation in ppmV readings due to background helium (naturally occurring He in the air, and any "spilled" helium released during hookup of test lines, venting from regulators, etc.) and a built in error due to the precision in measuring the flow rate in the sniffer tube. The ppm variation you speak of will (I think) be lost in the noise...

 

[NGiLuzzu]

To be precise, the LENNTECH converter I used and signalled above, considers Standard Temperature and Pressure (STP) defined as a condition of 100.00 kPa (1 bar) and 273.15 K (0°C), which is a standard of IUPAC.
I do usually neglect the difference between those STP's and the actual atmospheric conditions during the test, as I agree with btrueblood that the resulting error would be "lost in the noise" of the many other uncertainity sources...