Dear Spinlanders,
We are having problems with our variable temperature regulation using a liquid nitrogen heat exchanger. I wondered if anyone else had similar observations to what we’re seeing and could offer a possible solution? On a 1-year old Bruker NEO console equipped with a Smart Probe, we use a heat exchanger immersed in a 20-liter dewar of N2(l). The exchanger is similar to W124597 found on page 44 of the 2012 “Variable Temperature Control for NMR Probes User Manual” (P/N: Z33073), but has a ball-socket joint and 12-turn coil. Dry house N2 flows through this and into the probe. The heat exchanger has been in use since 2012. I have had no problems controlling the temperature from -100 C to 0 C in the past. Recently I have been unable to control the temperature, and I noticed the gas flow in the monitoring tab of EDTE was wildly fluctuating. When I remove the ball joint connector from the probe and observe the gas outflow at the socket, it is spitting out liquified nitrogen. This explains the variability of the flow and inability to maintain a temperature set point. I have never disconnected the joint before to observe the outflow, but I’ve also never had problems with the observed flow rate or temperature stabilization. I wouldn’t guess the N2(g) is present in the coils long enough to liquify at a 400 liter per hour rate. One hypothesis was that our heat exchanger had a leak. Immersion in H2O and pressurization did reveal a small bubble stream in one of our two exchangers. We tightened the fittings and removed the leak, but still observe liquid nitrogen spurting out of the ball joint connection when it is not connected to the probe. I have also made sure the inside of the coil is completely dry so that there is no constriction due to frozen water. Has anyone had similar problems, and if so how did they solve them?
Thanks for any help!
John
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John Grimes
Operations Manager
Department of Chemistry Instrumentation Facility
Massachusetts Institute of Technology
77 Mass. Ave. Rm: 18-0084
Cambridge, MA 02139
https://chemistry.mit.edu/facilities-and-centers/department-of-chemistry-instrumentation-facility-dcif/
T: (617) 253-4856
jgrimes_at_mit.edu<mailto:jgrimes_at_mit.edu>
Received on Thu Nov 07 2019 - 06:18:34 MST