🚀 go-pugleaf

In article <45b7cd$87e@cnn.Princeton.EDU> parris@ace.Princeton.EDU (Kevin D. Parris) writes:

>>In article <459370$prq@mark.ucdavis.edu> Hakon Hope writes:
>>I think it is unlikely that ice falling out of the transfer tube is the cause 
>>of the icing problem. It seems more likely that it is caused by turbulence. 

> Thanks for the reply.  We appreciate all input.
> However, there is ABSOLUTELY no question that our problem is being caused by 
> ice falling out of the transfer tube.  We are quite sure the flow is laminar.

Are you using the newer MSC design ?? In our setup, dating from early 1993,
the main dewar contains lN2, dry N2 gas from additional external dewars 
is supplied via the flow control into the dewar and hence onto the transfer
line. In the newer system, it appears that the external N2 gas supply has been
replaced by some other system that claims to be able to use compressed air.

With the old system, we have *never* seen ice from inside the transfer line
during active use (if we stop the flow abruptly and leave it off for some time,
we have seen some small ice blockages inside the line, occasionally, this 
being easy to clear by activating the heater inside the line).
We have seen the vacuum in the transfer line fail, requiring re-pumping, but
this manifests itself by a loss of ability to get to -180, and condensation
on the *outside* of the transfer line.  The only way, it seems to me, to get
ice formation on the inside of the transfer line is to have a too-humid
gas supply in the first place (not likely with the old setup involving 
evaporation of lN2).  Otherwise it would take an air leak of epic proportions
to allow room temp air to mix with the -180 gas flow to form ice xtals within
the transfer lines. The design of the transfer lines appears to be very similar
between the old and new units, and a leak in the transfer line would be
indicated by condensation. Have you tried changing the hoses for the gas
supply ?? Using lN2 dewars to supply gas ??

We do get ice build-up on the goniometer head from turbulent flow between the
inner cold flow and the warmer jacket flow, and at the end of the exit nozzle
if the warm/jacket flow is set too low, but that's the extent of our problems
(and this has been addressed previously by Hakon Hope).

Just my 2c,
Phil 
--
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| Phil Jeffrey                                  |                             |
| X-ray/Computer Manager, Crystallography Lab   | If you lie to the compiler, |
| Memorial Sloan-Kettering Cancer Center, NYC   | it will get its revenge     |
| phil@xray2.mskcc.org, p-jeffrey@ski.mskcc.org |     - Henry Spencer         |
| Ph: (212) 639 2189   Fax: (212) 717 3066      |                             |
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