Dear John,
I don't have any experience with recovery bags (ours are handled by
another department), but regarding the impurities I would even expect
the reverse effect from your hypothesis:
The impurities enter the bag via diffusion. Imagine part of your "lazy"
bag as completely cut off from the rest of the system, this would reduce
the diffusion-active surface area of the bag.
Now, this is certainly not entirely the case and there will be some gas
exchange with the "dead" volume. But still, at some point a diffusion
equilibrium with the air would be reached, and the closer the gas
composition is to that equilibrium, the slower the concentration of
impurities will increase inside the bag.
If you do not need the capacity of the bag, eliminating its surface from
the equation would obviously be beneficial in any case.
Best,
Matthias
On 18/07/2025 19:33, John H Grimes Jr. via groups.io wrote:
> Dear Helium Collectors,
>
> Our helium recovery system has three 30 m^3 bags that are connected with
> 47.5 mm ID stainless steel tubing running at floor level along an
> outside wall.See our homepage https://nmr.ccrc.uga.edu/ <https://
> nmr.ccrc.uga.edu/> ; in the background picture, 2 are hidden behind the
> magnet on the right, the third to the left. The two are about 50 & 75
> feet away from the compressor while the third is another 150 feet
> away.As can be seen they are suspended from a bar at the top.The gas
> connection is at floor level.Not surprisingly, they never empty (I don’t
> expect or want complete emptiness) as the helium makes a bulge at the
> top, but the bottom is sucked closed.I have observed that the bag
> furthest away never drains as much as the two closest to the compressor.
> There are 3 magnets that are upstream of this bag. I worry that this bag
> might be might be a greater source of impurities than the closer ones
> since the helium it collects is not exchanged as rapidly as the other 2
> bags.Does anyone else have a similar setup where some bags are closer to
> the compressor than others?If so, is my hypothesis valid?Are there any
> special cautions I should take for this bag such as pumping it down and
> closing it off when I do not need the extra capacity?
>
> Thanks,
>
> John
>
> John Grimes
>
> Complex Carbohydrate Research Center
>
> University of Georgia
>
> 315 Riverbend Road, Athens, GA 30602
>
> jgrimesjr_at_uga.edu
>
>
--
Dr. rer. nat. Matthias Brandl (he/him or they/them)
Technical University of Munich
TUM School of Natural Sciences - BNMRZ
Chair of Biomolecular NMR Spectroscopy (Prof. Sattler)
Lichtenbergstr. 4 (postal)
Ernst-Otto-Fischer-Str. 2 (physical)
85748 Garching b. Muenchen
Phone +49 89 289-52617
matthias.brandl_at_tum.de
https://www.sattlerlab.de/
https://www.bnmrz.org/
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Received on Tue Jul 22 2025 - 06:40:58 MST