Re: [Phys-L] compressed gas

["Dan L. MacIsaac" <danmacisaac@gmail.com>]

Possible relevant info:

To quickly fill SCUBA tanks you prefer not to directly fill from a 
compressor, or you get under-filled tanks due to the heat of 
compression / cooling issues described.  Hence a "hot filled" 
tank means it was pressurized from a compressor and is 
warm, so you don't have as much air as you think or
would like for going diving :^).  Hot fills are common out on the
islands away from the diveshop etc.

*****
Alternatively, you can fill with the tank sitting in a cold water 
pool/bath, or fill, wait and then top off after cooling.  
*****
Ordinarily SCUBA tanks are filled to 3000psi, tanks are 
tested to 5000psi every 5yrs.

Proper SCUBA fills are from a bank of (pre-)compressed tanks, 
at a rate of around 500psi/min, to a total of 3000psi.  So the
breathing gas is already temperature equilibrated at the
storage pressure.

Dan M, now wants to go diving...

Dan MacIsaac, Associate Professor of Physics, SUNY-Buffalo State College
462SciBldg BSC, 1300 Elmwood Ave, Buffalo NY 14222 USA 1-716-878-3802
<macisadl@buffalostate.edu>  <http://PhysicsEd.BuffaloState.edu>
Physics Graduate Coordinator & NSF Investigator for ISEP (MSP) and Noyce

On Dec 7, 2013, at 2:05 PM, John Denker <jsd@av8n.com> wrote:

> On 12/07/2013 01:34 PM, Carl Mungan wrote:
> > So yes, it's between zero and one-tenth. But much closer to zero than
> > to 1/10. I'm surprised.
>
> I betcha there are cooling fins on the back of the compressor.
> The manufacturer doesn't want the compressor to run at 3000K.
>
> Possibly constructive suggestion:  Get a length of high-pressure
> metal tubing, coil it up nicely, and submerge it in ice water.
> Put that in series with the rest of the fill plumbing, in the
> obvious way.
>
> Given that they're spending 20 minutes filling the tank, it
> shouldn't take too awfully much tubing.  If you decide you
> want more cooling, add more tubing in /parallel/ not series.
> That takes some fittings, but parallel works better than
> series:
> -- less impedance per unit surface area
> -- small diameter high-pressure tubing is muuuuch cheaper
>  than large diameter.
>
> If you manage to achieve too much cooling, it's super-easy
> to /underfill/ the cylinder, and let it warm up overnight
> to the desired nominal pressure and temperature.
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l