Re: N2 Cold exchangers
Ross Mair (rmair@stan.xx.swin.OZ.AU)
Sat, 16 Oct 1993 00:45:55 +1000 (EST)
Forwarded message:
> Date: Thu, 14 Oct 1993 18:12:13 +1000
> From: r.dancer@mailbox.uq.oz.au
> Subject: Re: N2 Cold exchangers
>
> >>Here in Iowa City for several months during each summer, neither the "cold
> >>dissipators" (made from an aluminum extrusion) from Bruker nor the sponge
> >>rubber pad trick prevents condensed water from dripping onto the magnet can
> >
> >I find the discussion most intruiging.
> >Yes... I've seen the same problem on a variety of Oxford magnets on Bruker
> >systems that I've used. I had always assumed dripping water was par for the
> >course on such systems.
> >
> >We have a Varian system, which uses a Varian egg-shaped magnet. Now, I know
> >these magnets have had their critics, but one thing it sure doesn't do is
> >drip water down the magnet from the nitrogen port.
> >
> >The N2 port is sealed with a cap (aluminium, I presume) from which
> >vaporizing N2 disappears down a tubing which feeds an N2 boiloff meter,
> >before being ported to the room. The only time ice may appears on this
> >tubing, or condensation occurs on the cap, is in the first 5 mins after a
> >liquid N2 fill, if the liquid N2 may have flowed longer than it needed to.
> >The rest of the time, the port is as dry as the rest of magnet. There is no
> >need for sponges, fins, heaters, or anything.
> >
> >Ross
>
> We have a Varian Gemini-300 and a Bruker ARX-500, and, indeed, we never see
> any build-up of condensation or ice on the Gemini, except briefly after
> some liq N2 fills. The Oxford magnet for the 500, however, has the
> customary "dribbles", despite the room in which it sits being
> air-conditioned and humidity-controlled to within an inch of its life! The
> only explaination I can suggest is that it may have something to do with
> the fact that on the Gemini the N2 dewar is marginally pressurised, and
> also possibly because the cap to the dewar is somewhat larger, allowing for
> better "dissipation of cold" (it usually feels about room temperature to
> the touch.
>
> I don't know if the above helps at all...
>
> Robert Dancer.
>
>