Randall Clague wrote:
>
> At 07:58 PM 06/05/2002, The Silent Observer wrote:
>
> >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.
>
> I'm not too concerned about water in the pressurant per se - that's a well
> known problem. What interests me is what effects we can expect from high
> pressure and very fast blowdown. I'm specifically thinking about ice in
> the lines.
I've seen ice form in pneumatic tools, working down from 120 psi to
atmospheric, at under 5 cfm flow, with ambient temperature around 50 F.
I've seen ice on the exterior of hose fittings in a 70 degree room with
similar pressure drop and flow of about 10 cfm. If I remembered my
thermodynamics from college, it'd be pretty easy to calculate the
temperature drop (don't forget to account for latent heat of evaporation
and latent heat of fusion as the water vapor goes through two phase
changes, both of which will release heat, i.e. keep the gas warmer) for
any given pressure drop and rate of gas release -- I think you'd just
need to multiply volume by pressure drop to obtain work done by the gas,
convert the work to heat, and then subtract that heat from the gas
(accounting for density or using mass flow rate, and accounting for
phase changes).
FWIW, carbon dioxide blowing down from the 800 psi tank at room
temperature gets cold enough to freeze some of the gas into dry ice; if
you chill the tank before you start, you've duplicated the commercial
method of making dry ice -- which sublimates about -80 F at sea level
pressure. With CO2, of course, the phase change from liquid to gas in
the tank helps things along...
--
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.
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