Randall Clague wrote:
>
>
> ...and I thought, hm, we have a professional rocket plumber right here on
> the list; let's ask him.
>
> What say ye? How much of a problem is water vapor in compressed air used
> as rocket pressurant?
Okay, I'm not a rocket plumber, but I do deal with compressed air and
systems that use it to do work every day -- I repair pneumatic nail guns
for a living. These tools use air at up to 120 psi (about 8 atm), and
in typical production applications are operating nearly as fast as the
compressor can pump. The air has plenty of time to cool by the time it
travels through the compressor's storage tank and 50 to 200 feet of hose
to get to the tool, and in the process some of the natural humidity is
dropped -- this is why compressor tanks must be drained periodically,
because the compressed air, once cooled back to ambient temperature, can
hold less water than at 1 atm.
Even though much of the water precipitates in the tank, there is still
some vapor in the air, and despite precautions like centrifugal water
traps, it's common to find condensation and even icing in the tools when
ambient temperature is as high as 50 F (10 C). And remember, this is
with the air expanding only from (at most) about 120 psig (8 atm) down
to ambient; though there'd be less water in the pressurant because of
the further reduced carrying capacity of higher pressure air, there'd
also be more cooling when the pressurant is released into the propellant
tank.
Condensation is also a problem with SCUBA tanks; if they're allowed to
drain off faster than the normal rate of breathing consumption there can
be enough cooling effect to condense liquid water in the tank and
promote corrosion. The analogy in the rocket would be condensation in
the pressurant tank.
Also worthy of note is that it takes several hours for a reasonably
portable compressor to pump a SCUBA tank up to 3000 psi (200 atm). This
is something you'd start the evening before a launch, not something that
you could reasonably initiate during the part of the countdown that
normally takes place at the range or test site.
--
Love wealth above life itself, and starve in splendor.
-- Elvish proverb
Donald Qualls, aka The Silent Observer NAR # 70141-SR Insured
Rocket Pages http://silent1.home.netcom.com/launches.htm
Telescope Pages http://silent1.home.netcom.com/astronomy.htm
Lathe Pages http://silent1.home.netcom.com/HomebuiltLathe.htm
Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.
_______________________________________________
ERPS-list mailing list
[EMAIL PROTECTED]
http://lists.erps.org/mailman/listinfo/erps-list
