[Beowulf] More about those underwater data centers

[John Hearns]

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 at 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-bounces at beowulf.org
> <beowulf-bounces at beowulf.org>] *On Behalf Of *Prentice Bisbal via Beowulf
> *Sent:* Tuesday, November 06, 2018 8:17 AM
> *To:* beowulf at 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
> sdm900 at gmail.com
>
>
>
>
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