[ausev] !12-volt A/C - scuba tanks can explode & dry ice notes

[tomsmail]

Go Tigers!

> :) Good questions.  Pardon me if I answer out of order.
>
> Fundamentally, the idea should be workable; however, there
> is a lot of energy stored when you compress gas and it has
> a nasty of habit of converting into to thermal energy when
> it is tapped quickly.  I read in last month's Pop Sci
> about a hybrid concept that was using compressed Nitrogen
> instead of the battery.
>
> The tank in question was a steel tank (not the more
> typical aluminum). Steel tanks have a higher risk
> exploding because the steel is less brittle than Aluminum
> (al).  Al tanks are more likely to crack/leak than
> explode.  Unfortunately, they are not very good with
> shock/vibration. That is why shop owners will visibly
> wince when you drop or bang the tanks.
>
> There are relief values, but they are a sort of last ditch
> back-up and (as my example shows) not always reliable.
> The show owner was right to be scared - they'd just put a
> hot pressurized can into a cold water bath.  Just think
> hot glass into ice water - steel can get brittle too.
>
> If you had an active system to monitor the max pressure
> then you could make this idea work. And you're right,
> bleed off the excess to cool the car in advance.
>
> I actually like combining the tank & dry ice idea.
> Converting solid CO2 into gas can generate pressure and
> cold!  It is also self regulating because increased
> pressure slows down the sublimation.  BUT - you'd need a
> special type of tank for it.  The ice would crack a steel
> or al tank if it regularly touched the sides.
>
> Sorry for the long reply - I've spent too long thinking on
> these issues in the past to be brief.  Feel free to send
> this up to the listserv if you want :)
>
> Rob
>
> -----Original Message-----
> From: tomsmail at wtez.net [mailto:tomsmail at wtez.net]
> Sent: Friday, August 25, 2006 12:59 PM
> To: rah at h-consulting.com
> Subject: Re: [ausev] !12-volt A/C - scuba tanks can
> explode & dry ice notes
>
> You gotta love the MEs - they're awesome!  Sometimes I
envy
> them too. (too bad for me I slept through Thermo).
>
> Question:  What about locating the tank UNDER the vehicle
> (in the shade)?  Also, aren't there pressure relief valves
> on those things? Also, what if you use half the volume in
> the morning on the way towork, and only half the volume is
> heated during the day?  Would that make a difference?
>
> What I'm suggesting is you have the thing recharged at 25
> deg C.  By the time you arrive at work the volume is 50%.
> By the time you are ready to go home the temperature is
> 50C so the pressure is back up to where it was in the
> morning with a full tank. Temp spikes above 50C are
> handled by venting (into the vehicle's cabin no less).
> Do you see any flaws with this?  Are the scuba tanks
> really that dangerous or was the scuba shop operator just
> being overly cautious?
>
> Thanks!
> Tom
>
>
>
>
> > WARNING: Scuba tanks do not do well sitting in hot cars.
> > Good old  Boyle's law (PV=nRT) means that the pressure
> > in the tank  will climb  quickly as it heats up and the
> > tank could EXPLODE.  That  is why they  fill tanks in a
> water bath at SCUBA shops.
>