Hi all,
I’m asking about the nitty gritty details of filling procedures while
connected to helium recovery. We made some troubling observations during our
most recent fill and want to identify/minimize risks for next time. It’s
a looong detailed story to read through. If anyone makes it to the end I’d
appreciate any opinions on what to change or if you agree with our conclusions.
My lab recently completed installing a full Quantum Technologies helium recovery system.
Each magnet’s helium exhaust port is connected to a copper header line via
manifold and long flexible whip. The header has a maximum pressure of 0.4 psi (before
triggering relief valve), and each magnet has its own one-way helium check valve,
15 mbar or ~0.2 psi. So at maximum I expect around 0.6 psi back pressure while filling.
Historically we applied ~1.2-1.5 psi on the transfer dewar without any issue. Fills
went smooth, magnets stayed happy. We employed that same procedure for our very first
fill test during the install after connecting to the header. At the end of the fill,
helium liquid came shooting out from the fill port upon removing the transfer line.
Not fun. This happened on both an Oxford 600 and Bruker Ultrashield 300. We attributed
it to the newly increased backpressure, and having to relearn when to stop the fill.
Hoping to prevent it from happening again, this week we opted to lower the pressure
on our transfer dewar. Our hypothesis being the magnet was accidentally over pressurized,
and our historic pressures were no longer appropriate given the new header connection.
So we used 0.9 psi on the Ultrashield 300 this week, and planned to lower it steadily
near the end of the fill to end more gently. Things went terribly.
Our helium level sensor usually “freezes” in the high 90’s for a few
minutes after putting in the transfer line stinger. As the fill progresses the sensor
unfreezes and provides a reliable impression of fill progress. This time it never unfroze
and we ended up flying blind from start to finish. After eventually accepting that we had
to operate without the sensor we decided to stop the fill early. Better to regain our
bearings than risk overfilling. During this discussion, the flexible whip started to
shake, which happens when liquid enters the line from the magnet and rapidly converts
to gas. This surprised us, by our estimates the magnet shouldn’t have finished
filling yet. We stopped the fill and removed the transfer line from the magnet. Liquid
came shooting out the fill port. Again, not fun. The helium level unfroze shortly
afterwards and came in at a mere 86%.
The helium level sensor freezes at filling start because the stinger coats the
thermocouple in liquid. It should unfreeze as the fill proceeds because that initial
liquid drains from the helium stack into the internal dewar. It shouldn’t remain
frozen unless liquid is trapped there, by say an ice block, or unless liquid reenters
the stack, preferably because full. Liquid can’t eject out the exhaust port
without climbing the helium stack, again preferably because full. But our sensor did
remain frozen, and liquid did come out the exhaust port. And at 86% the magnet is certainly
not full.
We concluded that the dewar pressure was too low. It couldn’t decisively overpower
the back pressure, and the tussle between the two pressure sources destabilized liquid
contents within the magnet. We think the liquid was sloshing dangerously. Perhaps there
are niche details when working on lower field superconductors with relatively small helium
volumes, we’re not sure. That all happened a couple days ago and not one user
complaint since. The magnet appears to be fine and we’re thankful we didn’t
quench. Next time we’re returning to our higher historical pressures and may
revisit the original plan to lower dewar pressure near the end for a gentle finish.
For those who read to the end you’re a saint. I’ll happily accept any
pointers and will attempt to answer clarifying questions. The situation spiked my
adrenaline to the roof, and I could do without that becoming routine. Happy magnet
happy manager.
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
mobile: (603) 953-5275
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#2248): https://urldefense.com/v3/__https://ammrl.groups=
.io/g/main/message/2248__;!!PvDODwlR4mBZyAb0!TBNyDWc5wEHfF7Snvm0lXWEOzvXxmg=
-Xv5olsqu9pC5gW4Hnx0tAeUSydY612TW5VBL6HVbDrIy_5AY49MSqhNcAMZJ3$
Mute This Topic: https://urldefense.com/v3/__https://groups.io/mt/112337799=
/7559972__;!!PvDODwlR4mBZyAb0!TBNyDWc5wEHfF7Snvm0lXWEOzvXxmg-Xv5olsqu9pC5gW=
4Hnx0tAeUSydY612TW5VBL6HVbDrIy_5AY49MSqhNZov_40$
Group Owner: main+owner_at_ammrl.groups.io
-=-=-=-=-=-=-=-=-=-=-=-
Received on Fri Apr 18 2025 - 13:22:15 MST