Hi there fellow spinlanders and helium recovery gurus!
I've been meaning to post this for a while now, though hoping to find a
solution prior to this, to no avail.
Here at the University of Vermont (UVM) we have a small scale helium recovery
system, manufactured by CryoMech, which is capable of producing 15L of liquid
per day (LHeP15). This system was installed in summer 2021, and aside
from several hiccups along the way, has been functioning well.
However, one major issue that we've been dealing with is that we haven't been
recovering steady state boil-off from the two NMR magnets in quite a while now
(at least several months). We have two NMR magnets connected to the recovery
lines (a Bruker Ascend 500 and an Oxford 500) and each magnet has it's own
manifold, with heat exchangers, etc. The copper piping leading into the
recovery room, which is in the basement, was installed when the building was
built in 2017. The other magnet that is connected to the system is part
of an MCD, which is cooled down and ramped up only when the researchers are
collecting data, and we also have an EPR that is hooked up, though used only
very occasionally. According to the magnet book for the two NMR magnets,
we should be boiling off about 0.6L of helium per day, or 4.2 per week total.
Unfortunately when I plot the totals in our recovery system, they are not
increasing, and the curve remains flat.
So....where is this helium going?
When I do the magnet fills, and there's a lot of pressure in the system, I
recover about 25L from filling both magnets. During the fills, I open
up the large flow meter for the large volume to flow through, while during
steady state the path goes through the smaller 'normal boil-off' meter.
We have a high quality helium gas detector, and I've wanded the manifolds on
numerous occasions. I have also followed the path of the pipes searching
for leaks, especially since there are at least two other labs that have
connections to the piping, although no instruments are hooked up there.
The ultimate test that we did to figure out if the piping is leaking, was
isolating the piping from just beyond the NMR magnet manifolds, all the way
into the recovery room in the basement, and pressurizing it with balloon grade
helium gas to 21psi. The 21psi pressure held for over 24h, which means
there's no leak in the piping leading to the basement. We've wanded
from the shut-off valve in the basement to the manifold where several lines
for the recovery system connect (leading into the bag, coming from the transfer
dewar) and haven't detected a leak there.
Our system does have a recovery bag, which sits in a room next to the recovery
system room, and an insulated hose (formal name?) leads into the bag, while
another one goes from the bag to the gas compressor, where the bag gas gets
compressed into cylinders. We have wanded the bag when inflated, wanded
the connections into and out of the bag, we've observed it fill up until it
hits the laser at the top, and didn't detect helium in the air when the bag
is completely inflated. Some oddities of the bag are that a couple of
years after the system was installed, somehow the bag was reseated and after
this it would never get as big as it did when it was brand new. Because
of this we lowered the location of the laser. Back when the system was
new, we'd let the bag inflate all the way, and once it would trigger the laser
at the top, the compressor would go on and the bag would be emptied. At
some point, for some reason, we thought that the bag was losing helium when
inflated, so a decision was made to 'bypass' (or empty) the bag daily during
the week. At that point we believed that that solved our recovery issues,
but when looking at the plots of the totals in the recovery system, it still
doesn't show that this is the case.
So... I am putting this out there to you, many of whom have a recovery system,
to solicit ideas of what I could try to figure out where this 0.6L per day are
going. Another test we thought of trying is to isolate and then inflate
the bag to see if we detect an obvious leak. Could this be done by just
shutting the compressor off, so that it doesn't start processing the bag once
the bag is full? And of course shutting a valve before the gas enters
the bag, and using balloon grade helium to pressurize the bag.
The steady state boil-off has got to be going somewhere. The 'normal'
boil-off flow meters do give a reading and this reading has been the same
since the system was installed. I'd appreciate any ideas/suggestions
that you may have!
Thank you and hope to see you at the Asilomar ENC very soon!
Cheers,
Monika
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Received on Thu Apr 02 2026 - 12:49:06 MST