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RE: [PSUBS-MAILIST] Inert gas
Thanks for the info Herve. Maybe CO2 and an emergency Air tank would be in
order.
Sincerely,
Greg
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Herve Jaubert
Sent: Friday, November 10, 2000 3:32 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Inert gas
Hi Greg,
I know one working sub with CO2 as of gas for ballasting, the gas is stored
liquid in a pressure tank.
But like Craig mentionned it , triple check should be done to verify that
there is no risks of asphyxiation. I d have to look into my adress book to
find the guy and his sub.
Though it is an excellente idea for emergency purpose, to inflate emergency
ballasts, lift bags or any other chambers, double walls, what ever, when
there is no other mean of surfacing. A small CO2 bottle has a huge lift
capacity by the volume of gas available. BUT the occupants of the sub must
learn the symptoms of CO2 asphyxia on humans to be able to recognize them in
case of a leak. Such situation is recoverable when detected.
Herve
----- Original Message -----
From: <CWall@swri.edu>
To: <personal_submersibles@psubs.org>
Sent: Friday, November 10, 2000 3:13 PM
Subject: [PSUBS-MAILIST] Inert gas
> Hi Craig - This may be a little off topic, but in all of this talk about
> propane, I began to wonder - do you know if anyone is using other
chemically
> inert gases for ballast purposes? I'm a little removed from my chemistry,
> but how about nitrogen or the like?
> I know you won't be able to use it as fuel, which would defeat your
> purpose - just wondering.
> Thanks,
> Greg
>
>
****************************************************************************
***
> ********88
>
> Greg, I'm probably the least qualified person here to address this, in
terms
> of what is actually out there, and the
> only answer I can give is that I don't know.
>
> While I can imagine that liquid nitrogen would have some advantages, it
> obviously wouldn't be plausible for durations beyond a couple days.
Another
> disadvantage is the other obvious point concerning the risk to the crew of
> asphyxiation, requiring plumbing isolation. All these points are
no-brainers,
> of course, so I'm sure I'm not telling you anything you didn't already
know.
>
> I do think, however, that there is a chance that it might have been used
on
> unmanned submersibles or possibly wet subs. I just flat don't know.
>
> For those who haven't thought about this, the choice of gases does
include the
> possibility of phase changes, which is a two-edged sword: nitrogen and
argon
> are still gases when compressed, and require strong pressure containers
for
> anything beyond small amounts- and while weight penalties in a sub are
> relatively moot, there is still a practical limit to the quantity that can
be
> carried. A liquid state would required cryogenic storage.
>
> For that you get much higher available pressures- warm the material or
open the
> valve, and you are able to blow ballast at significant depths.
>
> The problem with CO2 and propane, or other liquids that undergo a phase
change
> by liquifying, is that while you can carry much more quantity, the
available
> pressure is limited- for propane it's around 90 psi, and for carbon
dioxide up
> around 900psi. If you try to use propane to blow ballast much below
150ft, it
> will simply stay liquid. With CO2 the same thing occurs, but deeper. In
both
> cases you can overcome this by heating the liquid to get the vapor
pressure up,
> but that takes a lot of heat....and if it cools off again, it condenses.
>
> Of course, you can blow a LOT of ballast from a liquified gas--- but it
has to
> turn into gas to be useful......so I suspect that most applications that
would
> use an inert or unreactive gas would be either one-shot (emergency type
> applications) or shallow water (to cope with the pressure limit to
> vaporization). And in most cases I suspect (but I don't know) that these
would
> be for unmanned vehicles.
>
> Hope that is useful- it's nothing anyone who has had chemistry wouldn't
know,
> so it's probably fluff at this point.
>
> Craig Wall
>
>