Thinking about liquid cooling , and the ebuillient cooling, the main
sources of heat on our current architecture servers are the CPU
package and the voltage regulators. Then the DIMMs.
Concentrating on the CPU die package, it is engineered with a flat
metal surface which is intended to have a thermal paste to transfer
heat across to a flat metal heatsink.
Those heatsinks are finned to have air blown across them to transport
the heat away.
In liquid immersion should we be looking at having a spiky surface on
the CPU die packages and the voltage regulators?
Maybe we should spray the entire board with a 'flocking'' compound
and give it a matt finish!
I am being semi-serious. I guess a lot of CFD simulation done
regarding air cooling with fins.
How much work has gone into pointy surfaces on the die package, which
would increase contact area of course and also act as nucleation
points for bubbles?
One interesting experiment to do - assuming the flat areas of the CPU
in an immersive system do not have (non thermal paste) heatsinks
bolted on:
take two systems and roughen up the die package surfacewith sandpaper
on one. Compare temperatures.
ps. I can't resist adding this. Sorry Stu .
https://www.youtube.com/watch?v=kHnifVTSFEo
I guess Kenneth Williams is a typical vendor Site Engineer.
pps. the actress in the redress had her career ruined by this film -
she ver got a serious role again after perfectly being typecast.
On Tue, 6 Nov 2018 at 22:57, Prentice Bisbal via Beowulf
<beowulf@beowulf.org <mailto:beowulf@beowulf.org>> wrote:
On 11/06/2018 02:03 PM, Lux, Jim (337K) wrote:
True enough.
Ebullient cooling does have some challenges – you can form vapor
films, which are good insulators, but if you get the system
working right, nothing beats phase changes for a heat transfer.
If I recall what I learned in my Transport Phenomena classes in
engineering school, you need a reasonably high temperature
difference to get a stable film like that. For that to happen,
radiant heat transfer needs to be the dominant heat transfer
mechanism, in the range of operation we are talking about, the
temperature difference isn't that great, and conduction is still
the dominant form of heat transfer.
Here's an example of what 3M Novec ebullient cooling looks like.
It doesn't look like it's anywhere near the film boiling regime:
https://www.youtube.com/watch?v=CIbnl3Pj15w
--
Prentice
*From:*Beowulf [mailto:beowulf-boun...@beowulf.org] *On Behalf
Of *Prentice Bisbal via Beowulf
*Sent:* Tuesday, November 06, 2018 8:17 AM
*To:* beowulf@beowulf.org <mailto:beowulf@beowulf.org>
*Subject:* Re: [Beowulf] More about those underwater data centers
. And serviceability is challenging. You need to pull the
"wet" boards out, or you need to connect and disconnect
fluid connectors, etc. If you're in an environment where
you can manage that (or are forced into it by necessity),
then you can do it.
I think everyone on this list already knows I'm no fan of
mineral oil immersion (It just seems to messy to me. Sorry,
Stu), but immersion cooling with other liquids, such as 3M Novec
engineered fluid addresses a lot of your concerns. It as a low
boiling point, not much above room temperature, and it was
originally meant to be an electronic parts cleaner (according to
a 3M rep at the 3M booth at SC a few years ago, so if you pull a
component out of it, it dries very quickly and should be
immaculately clean.
The low boiling point is an excellent feature for heat transfer,
too, since it boils from the heat of the processor (ebullient
cooling). This change of state absorbs a lot of energy, making
it very effective at transferring heat away from the processor.
The vapor can then rise and condense on a heat exchanger with a
chilled water heat exchanger, where it again transfers a lot of
heat through a change of state.
Prentice
On 11/05/2018 06:30 PM, Stu Midgley wrote:
I refute both these claims.
You DO want to run your boards immersed in coolant. It
works wonderfully well, is easy to live with, servicing is
easy... and saves you almost 1/2 your power bill.
People are scared of immersion cooling, but it isn't that
difficult to live with. Some things are harder but other
things are way easier. In total, it balances out.
Also, given the greater reliability of components you get,
you do less servicing.
If you haven't lived with it, you really have no idea what
you are missing.
Serviceability is NOT challenging.
You really do NOT want to run boards immersed in coolant
- yeah, there's folks doing it at HPC scale
Whatever the coolant, it leaks, it oozes, it gets places
you don't want it to go. And serviceability is
challenging. You need to pull the "wet" boards out, or
you need to connect and disconnect fluid connectors,
etc. If you're in an environment where you can manage
that (or are forced into it by necessity), then you can
do it.
--
Dr Stuart Midgley
sdm...@gmail.com <mailto:sdm...@gmail.com>
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