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On Wed, 13 Aug 1997 pdisler@io*.ne* wrote:
> Chuck wrote a very well put together post on some of the possible failure
> modes that may occur when introducing pure O2 into a scuba cylinder. I will
> add that I'm in full agreement with same.
I still don't have an opinion on O2 cleaning and stuff. I'm inclined to
think that more precautions are not a bad idea but I also think that
pushing O2 cleaning for the wrong reasons is not productive. I see
two big problems with the reasoning behind the original "O2 clean - very
long post !".
1) Heating by turbulent flow????
Unless I don't understand something fundamental, turbulences can not
selectively compress gases. A turbulent flow will cause just as much
compression as expansion and hence no net heating is due to turbulence.
2) Heating by deformation of the cylinders???
Come on! that does not generate any significant amount of heat.
Room temperature is way more important than that! If any cylinder
deforms enough to generate any heat it's probalby time for an hydro
(which it's bound to fail).
In all this debate, the only "significant" heating source that I
am semi-convinced exists is that generated by the impact of a
super-sonic compression wave against obstructions (tight bends).
These are generated by the rapid opening (and almost instantaneous
gas line pressurization) of a "ball type" valve. These can be treated
as "adiabatic" since everything occurs in a fraction of a second.
Once the line is pressurized I don't see how "local turbulences"
could create the kinds of temperatures comparable to that of shock waves.
The only usefullness that I see to needle valves is to prevent
the instantaneous pressurization of the gas lines. Once the line is
pressurized, I don't see how the heat generated by rapid filling of
cylinders can cause any problem. And this seems to be confirmed
every day by the gaz suppliers who fill O2 cylinder in a matter of
seconds. This process if far from adiabatic or you would not
feel the heat on the cylinder...
BTW: are 02 gas cylinder valves? needle valve? Don't think so!
BTW2: needle valves a filling whip only move the problem upstream.
ie you still have to open the 02 supply tank valve
I'd really like that somebody told me that I'm wrong but please don't
confuse turbulence and shock wave compression like is done on this
"spacecraft line" of the original post.
[\]
|
=================================================================^^(_)^^^^^^^^^
Roger Lacasse "I found the meaning of life!
Foster Radiation Laboratory, It's in the eyes of my wife and kids."
McGill University, Office: (514) 398-7025
3559 University street, Fax: (514) 398-7022
Montreal, Qc, Canada. e-mail: roger@ph*.mc*.ca*
H3A 2B1 http://spiff.physics.mcgill.ca/scuba.html
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