[Beowulf] More about those underwater data centers

[Prentice Bisbal]

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] *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 <mailto:sdm900 at gmail.com>
>
>
>
>
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