Gauge Pressure usage in Gas Mixtures
Gauge Pressure usage in Gas Mixtures
(OP)
I guess I need a refresher. I have a 2 part gas mixture (40% Pa and 60% Pb).
I know that the total fill pressure is 10 bar absolute.
I need to fill with Pa first using gauge pressure. I was told that I have to subtract atmospheric pressure from the partial pressures of Pa and Pb to determine the patial filling pressures using gauge pressure. I do not think this is correct since I would be subtracting atmospheric pressure twice (3 bar rel. of Pa and 5 bar rel. of Pb) which cannot be summed to get the total filling pressure in gauge (9 bar rel.).
[Ptotal = 10 bar abs = 4 bar abs (Pa) + 6 bar abs (Pb)
my point: Ptotal = 9 bar rel = 3.6 bar rel (Pa) + 5.4 bar rel (Pb)
the other person's point: Ptotal = 9 bar rel but the partial pressure uf Pa is 3 bar rel and the partial pressure of Pb is 5 bar]
Who is right?
I know that the total fill pressure is 10 bar absolute.
I need to fill with Pa first using gauge pressure. I was told that I have to subtract atmospheric pressure from the partial pressures of Pa and Pb to determine the patial filling pressures using gauge pressure. I do not think this is correct since I would be subtracting atmospheric pressure twice (3 bar rel. of Pa and 5 bar rel. of Pb) which cannot be summed to get the total filling pressure in gauge (9 bar rel.).
[Ptotal = 10 bar abs = 4 bar abs (Pa) + 6 bar abs (Pb)
my point: Ptotal = 9 bar rel = 3.6 bar rel (Pa) + 5.4 bar rel (Pb)
the other person's point: Ptotal = 9 bar rel but the partial pressure uf Pa is 3 bar rel and the partial pressure of Pb is 5 bar]
Who is right?





RE: Gauge Pressure usage in Gas Mixtures
RE: Gauge Pressure usage in Gas Mixtures
If so, then going to 3 bar(gauge) with A and to 9 barg with B gets you to the 60 40 mix.
David
RE: Gauge Pressure usage in Gas Mixtures
RE: Gauge Pressure usage in Gas Mixtures
When I was in school (think slide rules), we used the term "atmosphere" which was never defined as precisely as "bar" is defined in common usage today--but there was never any confusion about "gauge" and "absolute" because "atmosphere gauge" had no meaning. We've had this discussion many times in eng-tips.com about "what does a pressure gauge read at zero barg?". Some say zero. Some say 14.5 (psia) minus local atmospheric pressure. I don't think that there is an official answer to that question, but if it not the later then you get some squirrely results in vacuum situations at high elevations (where I live).
The fact that you are using a yardstick with the first foot cut off is not germane to how high the wall is.
David
RE: Gauge Pressure usage in Gas Mixtures
Thanks.
RE: Gauge Pressure usage in Gas Mixtures
Regards
RE: Gauge Pressure usage in Gas Mixtures
If I recall correctly we filled the majority of the cylinders using pressure gauges in absolute pressure. The higher pressure gauges were Heiss gauges which I don't think were absolute.