Hi All,
Here is the summary of the replies I received on my request for "solutions"
to fouling of the external compressor for our cryoprobe. My goal was to
avoid a gradual or sudden diminishment of the heat dissipation ability of
our compressor. I was thinking of the super coarse old style of filament
furnace filters to minimize the restriction but it seemed like they were
hard to find plus it would be better to have a larger cross section for air
filtration. So I looked at what is call expanded metal or perforated
aluminum. I was going to put that together but then started thinking I
would need it to be easily removable for those times I need to actually
clean the fins and the project kind of expanded. I spoke to a local Bruker
engineer and was told I can hose the unit off while operational. Sounds a
little scary to me but it is an outdoor rated unit and can handle driving
rain. I may try this (with rubber gloves on)
But then the computer on our 600 died and I turned my attention to building
a new PC and upgrading to TS 3.6. We had some other changes that had to be
rolled out with that change so I got delayed. For some reason stuff I
thought NMRSave would back and overlay from 3.2.7 onto 3.6 up did get
created in the new Topspin build. In particular probe list and my prosol
tables were not there.
The good news is that this has been the mildest cottonwood season I have
seen here, almost no "cotton" from the trees. Hopefully it is not just
late.
Thanks to all who took the time to reply to me!
Joe
My original post:
We are getting ready to install our cryoprobe for a few months. We are
located in a beautiful location right along a river which is lined with lot
of stately cottonwoods. Unfortunately in a few weeks it will look like a
pretty nice snowfall is happening when it is really just "cotton" from
the cottonwoods. I saw a note in the logbooks from a predecessor here
saying that the cryoprobe was thermally cycled to allow cleaning of the
outdoor compressor due to the cottonwood issue. I expect that the air flow
is just too high to allow a shop vacuum to succeed at pulling
the cotton off of the cooling fins while the fan is operating. I am
thinking of trying to build an external cage with screening to allow for a
larger cross section for air flow or to install a slip-in holder for a
coarse external filter.
1. Have users been able to pull debris like this out of the cooling
units fins while the fans is in operation with a good shop vacuum?
2. Has anyone built an external filter holder, I know that it would have
to be the coarse fiber style filter, that paper would be too restrictive.
3. Has anyone built an external "cage" with screening and if so was it
coarse wire or normal window screening
I will post a summary if anyone has created a solution for this issue.
Thanks
Regards,
Joe
Thanks to all who answered, Heather Schenck, Rainer Haessner, Gary Strahan,
Ronald Shin, Dean Olson, Dmitry Pichugin, Dave Vander Velde, Dave Rice,
Jerry Hirschinger, Bob Berno, Rich Shoemaker
Replies
A fine filter is wise. We kept losing the cooling in our facility (in the
old building) because the AC on the roof would get clogged with
cottonwood seeds
every year. It was on the roof of the 4th floor! Good luck.
------------------------------------------------------------
that's no big act.
Take that type of brush to clean flasks inside and rinsing water and clean
the heat exchanger from the backside of the compressor. No need to stop the
compressor, don't worry about all the water dripping inside the compressor
housing.
------------------------------------------------------------
I have a somewhat similar problem, as our HVAC air handler is at ground
level and sucks in all kinds of wonderful stuff, from grass and leaves to
just dirt. Our facilities people have put a lot of filters on it and built
a large coarse box around it. It seems as though they have finally got it
so that it doesn’t have significant problems.
Of course, this is just a HVAC intake. Your compressor will be more
sensitive.
----------------------------------------------
The outdoor compressors aren’t really cleanable using just a vacuum. The
dirt and dust, along with any other particulates you can imagine, are going
to cling to the coils pretty tightly (not just the fins), and they tend to
stick quite stubbornly, especially when you combine fibrous material with
conventional dirt and dust. While you may be able to get some of the
material out, the bulk of it will stay adhered to your coils.
We’ve been having to clean off the compressor coils every 6 months or so,
since the University has had a lot of construction going on adjacent to us,
which kicked up a lot of particulates that can lead to a compressor
overheating and shutting down, and it’s simply best to warm up the
Cryoprobe and clean it off with Nu Brite.
You’re going to be best off using a foaming alkaline cleaner at least twice
a year (although the engineer that Bruker sends will clean it off for you
as part of the annual Cryoprobe maintenance service), and Bruker recommends
using Nu Brite outdoor coil cleaner (comes in a blue liquid concentrate).
The foaming action literally rips off the junk from the coils, and pushes
it out of the fins.
Besides, it’s usually a good idea to warm up the Cryoprobe at least once
between yearly services, so that you can pump out the accumulated moisture
before too much accumulates.
---------------------------------------------------
I think a vacuum cleaner will work. Really. It might not work if you wait
too long and a mat forms. “Vacuum early. Vacuum often.” Just like voting
in Chicago. (Hey, I’m from Chicago we never voted early, but how often was
a bit complicated [(“your age” – 18)/5) then rounded up because we knew
wisdom comes with age] 😏
-----------------------------------------------------
Previously I was able to use a shopvac (I think it is the 8 gallon one)
with a soft bristles attachment from a regular vacuum cleaner to get all
sort of junk off the sumitomo outdoor units. We would take the little
plastic protector off and gently scrape along the metal fins. It takes a
while but it worked out for us so far.
Hi Joe, My experience at Kansas was that I had to warm up the cryoprobe
every 3-4 months because its efficiency would drop over time and the heater
power used to keep it at a constant temperature would decline. While it was
warm, I would throw the breaker on the outdoor unit and wash it down with a
garden hose, then let it dry out before turning everything back on. We were
in an interior courtyard and got a fair amount of trash, leaves, and pigeon
feathers as well as dust. We didn't have a cottonwood season, however.
--------------------------------------------
Hi – instead of stately cottonwoods our problem at Merced is central-valley
dust. Our outdoor
water chiller cools our indoor Helium compressor. We buy preventative
maintenance from a
local air conditioning company and they can usually work around the moving
fan. We warm up
only if necessary. I have given thought to nylon netting on the walls of
the enclosure (we have a roof).
How about one of those outdoor bug-screening vacation cabana’s
for cottonwood season? I have
worried that a slip in furnace filter might be too much for airflow – but
maybe not?
-------------------------------------------------------------
Hi Joe,
You might just cover the coil with coarse filter blanket, and let the fan
suction hold it in place (NOT!). The fact that the fan suction holds up
the filter batt is a good sign there is significant restriction of air.
Cryo-compressors are very touchy regarding heat, so I’d be reluctant to
restrict the air much at all. Heat breaks down the compressor oil, and the
volatile compounds that result contaminate the helium lines.
So, that leaves you with building a large cage, IMO. Window screen might
be all you need with no filter batts. It would be easy to bend around and
fasten to a wood frame.
If using rolled bulk filter media, I’d back it with ½” ‘hardware cloth’ for
free airflow, rather than window screen. I’d simply tie-wrap the filter
media to the hardware cloth, and clean them with a vacuum, rather than
disturbing the accumulated mess by trying to slip a full filter out of a
slot. Hardware cloth is strong enough to shape and tie into a box without
wooden support. IMO the coarse pre-filter should have 3-4 times the
surface area of the coil in order to keep good flow.
Just my opinion, not experience. We have water-cooled compressors here.
------------------------------------------
My cryoprobes are water cooled, so I can’t really help you.
I think you are taking the right approach: use some kind of cage/screen to
help filter the larger particles from clogging the fins of your heat
exchanger. But as you say, the key thing will be to be able to maintain
sufficient airflow even when the screen starts to get clogged.
How much room do you have? Can you build a rather large cage? I’m think
something that might look like a small greenhouse (made of screens instead
of glass panels) around the cryoprobe cooling fins, but large enough that
you can stand inside.
That external screen-cage sounds like a good idea, since I had to have our
condensing units at CU Boulder power-washed every year after the
Cottonwood bloom!!
I suppose it might help a lot, as long as the airflow into the compressor
is not restricted.
*******************************
Joe Dumais, Ph.D.
Associate Research Professor/Nuclear Magnetic Resonance Spectroscopist
Boise State University
College of Arts and Sciences
Department of Chemistry and Biochemistry
1910 University Drive, Boise, Idaho 83725-1520
(208) 426 4913
http://chemistry.boisestate.edu/
*******************************
Sent from my MS Windows PC
Received on Thu May 23 2019 - 10:45:29 MST