{Spam?} Re: AMMRL: The big OOPS
Charles L. Mayne (mayne@chem.utah.edu)
Fri, 28 Dec 2007 19:14:08 -0700
Hi Bob,
Do we really know that these materials are insoluble in liquid helium?
I have not seen any data on the subject; maybe some of the group knows
the answer.
Passing warm argon into the storage dewar would undoubtedly evaporate
enough liquid helium to pressurize it for the transfer, but is the
argon totally insoluble in the liquid helium. If not, argon could be
transferred into the magnet and remain there, being less volatile than
the helium. As you say, this probably has no bad consequence unless
there is a lot of it.
Charlie
Charles L. Mayne
University of Utah
Department of Chemistry
315 S 1400 E
Salt Lake City, UT 84112-0850
Room b473 HEB
voice: 801-581-7413
FAX: 801-581-8433
On Dec 27, 2007, at 1:21 PM, Silverman, Bob wrote:
> Dear Jane and Group,
>
> In giving these issues some thought, I don't believe that there
> should be any harm in using a low grade of helium gas to pressurize
> a liquid helium dewer. The typical impurities in helium gas are
> nitrogen and hydrocarbons. The tiny amount of either of these that
> contacts the surface of the liquid helium will solidify. Assuming
> that the helium dewer is not emptied in the fill process (I always
> arrange for this never to happen.), and knowing that any
> contaminants will freeze out of the liquid, then only ultra pure
> helium will transfer into the magnet. I guess it is possible that a
> "spec" of frozen material could get swept into the liquid stream but
> this should sit on the bottom of the magnet helium can and cause no
> problem. Most, if not all, of the miniscule amount of oil residue
> will go back to the liquid helium supplier.
>
> The same could probaly be said about using gases other than helium
> for the transfer although I don't feel that this should knowingly be
> done since this might produce a significant amount of solids at the
> bottom of the delivery dewer. In all instances the liquid helium
> dewer acts like a big cold trap!
>
> Happy New Year to all,
> Bob Silverman
> UCLA
>
> -----Original Message-----
> From: Jane Strouse [mailto:strousej@chem.ucla.edu]
> Sent: Wed 12/26/2007 12:43 PM
> To: ammrl@ammrl.org
> Cc:
> Subject: AMMRL: The big OOPS
> Dear AMMRLers,
>
>
>
> I indirectly received the message below from someone who was
> pretty
> embarrassed about having used the wrong gas to pressurize the storage
> dewar for helium fills. I thought I would relate my experience with
> this sort of thing. Quite a number of years ago, I found that the
> people working for me had been using nitrogen gas. I have no idea how
> long this had been going on or how it happened that we ended up with
> nitrogen rather than helium on the cart we use for fills.
> Amazingly, we
> seemed to have not observed any ill effects from this. I thought
> about
> it and decided that if you really did your fills correctly, you could
> get away with this, because none of the gas should enter the transfer
> line, and if the line is sufficiently above the bottom of the storage
> dewar, any condensed nitrogen would not be pushed into the transfer
> line. At any rate, we did later de-energize a couple of the solenoids
> to move them to a new building. There was no problem whatsoever with
> putting in the charging rods, so if there was icing from the nitrogen,
> it was not substantial. (Of course, it is possible that the tank had
> just been put on the cart when I noticed it and was never used, but I
> always presumed it had been used.)
>
>
>
> This leads me to another question. I once had a mass spec service
> person tell us that we should use ultra-high purity helium (UHP,
> 99.999%) for the liquid helium transfer into an FT-MS solenoid. I
> thought he was crazy, but I supppose it is possible that it would be
> better for that particular magnet. Do any of you use UHP helium gas
> for
> transfers? We certainly do not.
>
>
>
> Jane Strouse
>
>
>
>
>
>
>
>
>
> Message received:
>
> ________________________________________________________________________
> _______
>
> Dear Spinners,
>
>
>
> First of all, happy holiday season!!!
>
>
>
> I have been a passive observer and certainly taking advantages of the
> fruitful discussions at AMMRL. Here is a story that I feel I can
> use to
> contribute to the community. I am very much embarrassed in making
> such
> mistake, as you can see I am even hiding my name, but I still want to
> post it, so everyone could learn something from it.
>
>
>
> I have been filling liquid helium to my 400 MHz magnet by myself and
> for
> the past two years I thought that I have been using helium gas to
> pressurize the tank (well, read the label before using it). Just a
> few
> days ago, I found that it had been argon gas all along. Before using
> this gas cylinder, there had been no problem doing it and after
> switching to the tank, I started experiencing technical problems and I
> blamed the liquid helium supplier and moisture in the air. Here were
> the problems: (1) the liquid helium inlet (on the magnet side)
> seemed to
> be "ice" blocked, (2) it took from one to two hours to fill it, and
> (3)
> at the end of the filling process, it was extremely difficult to pull
> out the transfer tube (somehow the tube got stuck somewhere in the
> system on the magnet side and especially on the liquid helium tank
> side
> - I even destroyed one of my transfer tubes to pull it out). Of
> course
> the root of the problems is that the argon gas solidified in the
> system.
> Just last week, I found the mistake and switched to helium gas;
> everything goes back to normal now.
>
>
>
> So, what can we benefit from such odd experience? Although some might
> think that there are other factors to consider, from the experience I
> believe that we don't need ultra high purity helium gas at all for the
> refilling. A regular grade helium gas will do the job just fine. The
> gas I used is almost 100% purity argon and it has been two years.
> If it
> doesn't hurt the magnet this way (in terms of building up alarming
> level
> of solids in the magnet or clogging the system permanently), why we
> need
> to use ultra high purity helium gas? By the way, the boiling point of
> argon is about -186 C, oxygen is about -183, and nitrogen is about
> -195
> C.
>
>
>
> Anyone cares to shed some more opinions?
>
>
>
>> From someone too embarrassed to show his/her name.
>
>
>
> ________________________________________________________________________
> _______
>
>
>
>
>
>
>
>
>
>
>
> ----------------------------------------------------------------------
>
> Dr. Jane Strouse
>
> Director, UCLA Molecular Instrumentation Center
>
> 1410 Molecular Sciences Building
>
> Los Angeles, CA 90095-1569
>
> (310)-825-9841 - voice
>
> (310)-825-2280 - fax
>
> strousej@chem.ucla.edu
>
> http://www.mic.ucla.edu
>
> ----------------------------------------------------------------------
>
>
>
>
>
>
>
> ----------------------------------------------------------
> IMPORTANT WARNING: This email (and any attachments) is only
> intended for the use of the person or entity to which it is
> addressed, and may contain information that is privileged and
> confidential. You, the recipient, are obligated to maintain it in a
> safe, secure and confidential manner. Unauthorized redisclosure or
> failure to maintain confidentiality may subject you to federal and
> state penalties. If you are not the recipient, please immediately
> notify us by return email, and delete this message from your computer.
> ----------------------------------------------------------
>
>
>
> --
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.
>
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.