Dear all,
I hope that everybody is doing well.
Recently one of our magnets (Bruker Ultrashield 400 WB Plus ) has shown a strange behavior and I would like to know if anyone has encountered similar problems:
About 1 hour after a regular Nitrogen fill the pressure in the nitrogen dewar rises, which is observed by freezing in the lN2 fill ports and a noticeable outflow of nitrogen gas. At the same time the Helium boil-off measured with the regular flow meter rises to 3-5x the regular value.
We have addressed the problem by releasing pressure through the removal of the heat exchangers at the fill ports for around 2 hours (i.e. the lN2 dewar was left open). After this, the magnet settles and it returns to regular boiloff rates
During regular operation the heat-exchangers at the fill ports are connected via tubing, which end in a check-valve. I believe that the problem was originally caused by a failure of this check-valve, which we have since replaced. We also inserted a suitable rod to check for internal icing within the Ln2 dewar. There was no indication of icing.
Has anybody seen such a problem? Would you know its cause? Any fixes?
Thank you for any insight,
Hanno
______________________________________________________________
Johannes Leisen, Dr. rer. nat.
Principal Research Scientist
Georgia Institute of Technology
Atlanta/GA 30332-0295
Tel. 404-894-9241 (office: MoSE G113b)
404-894-1827 (NMR lab: MoSE G143)
404-385-3894 (MRI lab: IBB 0404)
Received on Thu Mar 21 2019 - 09:48:18 MST