Re: Probe temperature control...

G. Pearson (gpearson@blue.weeg.uiowa.edu)
Wed, 22 May 1996 12:21:53 -0500


Hi.

I'd like to try out a Neslab # CC 65 II for NMR sample cooling. Perhaps you
guys who already use this can answer a few questions for me.

1. How long is the (insulated) air line which runs from your heat exchanger
(with isopropanol, etc.) and the probe?

2. How far from the magnet do you have the CC 65 II box?

3. Is the hose and/or cold finger non-magnetic?

Thanks in advance for the information! -- Gerry


FWIW: VORTEX TUBES
^^^^^^^^^^^^^^^^^^^^
We have for many years used vortex tubes to supply cold air to the NMR probes.
_Much_ more convenient than an ice chest with copper tubing in it. We feed
them air at about 3 atmospheres gauge pressure & dew point of -15 C at roughly
2000 liters/hr. [atmospheric-pressure flow rate], and they supply cold air to
the probes. (We can only get down to about +10 C in a Bruker (supercon
magnet) probe, but we used to get sample temperatures down to about -5 C in a
Jeol FX90Q) After some rather tedious initial adjustments, they are
essentially trouble-free, requiring only occasional cleaning every few years.
The thing I do _not_ like about them is that they don't cool very well at all
unless the gas flow rate to the probe is high enough to cause some spinning
problems in our current probes. That's why I'm looking for alternatives.

Vortex tubes are sometimes called Hilsch tubes or Ranque tubes. Using
information from Hilsch's article (1), I designed one, had a machinist make
it, and it did a good job cooling the probe of a Bruker HX-90E as low as -10
C. Since around 1980, we've purchased our vortex tubes from Vortec Corp. in
Cincinnati, Ohio, USA. These are completely non-magnetic -- stainless steel,
brass, and plastic. They used to cost < $200 each, but that was more than a
decade ago.

(1) Rudolf Hilsch, "Die Expansion von Gasen in Zentrifugalfeld als
Kaelteprozess", Z. Naturforschung, 1, 208-214 (1946)
---------------------------------------------------------------
Gerald A. Pearson INTERNET: gerald-pearson@uiowa.edu
Chem. Dept., Univ. of Iowa OFFICE: 319-335-1336
Iowa City, IA 52242-1219, USA LABS: -1332, -0073 FAX -1270
---------------------------------------------------------------