Re: [PSUBS-MAILIST] The problem with propane for blowing ballas

[CWall@swri.edu]

As a matter of fact, it was my CRC where I found propane listed as soluble in
water.

You are right, of course, that propane is non-polar and thus is not capable of
forming hydrogen bonds or strong dipolar interactions.  But it is a small
molecule, and there is in increased propensity to disperse without forming a
bubble.  The question is: how significant is this?

For me, it amounts to this- at some depth ABOVE that at which no pressure
differential exists to move the propane out of the bottle and into the ballast
tank, the propane would fail to form bubbles but would simply come out of the
line as liquid and fall through the ballasts tank and right on out the bottom. 
  At what depth would this occur?  Who cares!   It will be related to
temperature and other dissolved constituents as well, but the unpredictability
is the thing- even if you find or observe the exact equilibrium
properties....it won't have a chance to GET to equilibrium before it falls out
the bottom of the ballast tank.

IOWs, I didn't see much value in going after an accurate prediction of when
this would occur and when it wouldn't- the point is, it's probable that you'd
lose some of the performance at depth if the propane was allowed to contact the
 water in a liquid form, and going to a bladder solved both this and the hatch
problem (i.e., the need tor a gas-tight ballast tank hatch if a bladder wasn't
used and the replaceable propane tanks were mounted inside the ballast tank).

 So yeah- the solubility might be slight- but introducing liquid propane (worst
 case) or even gassified propane would reduce the depth at which you could blow
 a bubble into water, and that is enough for me- I'll go to a bladder, with the
 backup of a well sealed but convenient hatch- as opposed to a hatch that is
expected to be gastight enough to be a primary containment barrier.  (The
bladders have their own problems, but I expect them to be manageable with
frequent replacement intervals and good inspection procedures..)

Craig Wall
---------- Original Text ----------

From: "John Brownlee" <jonnie@cobweb.scarymonsters.net>, on 11/17/00 4:59 PM:
To: Incognito2@CTC@SwRI26[<personal_submersibles@psubs.org>]

	Don't have my CRC with me on the road, but I'll bite.

	The solubility of propane, a non-polar molecule, is something
(from memory here) like 6cc/L water at 15C. This is sparingly soluble for
a gas in a liquid, and not too different from oxygen (or air for that
matter). CO2, which can be a ballast gas, has a solubility 10+ times
this at ~90cc/L. 
	I am not infallible, but last I checked like dissolves like and
water is polar, propane non-polar. I would expect the solubility to be the
same magnitude of air. This does not affect the fact that I wouldn't do
this myself for myriad other reasons. Unless those -HS groups on mercaptan
odorant are working in some way I don't know about, I think the solubility
is not the show-stopper.
	

							John

John Brownlee
Chief Systems Administrator
Scary Monsters Network
jonnie at scarymonsters dot net