[Beowulf] bring back 2012?

Prentice Bisbal pbisbal at pppl.gov
Fri Aug 19 10:49:53 PDT 2016

On 08/19/2016 12:10 PM, Stu Midgley wrote:

>     I think direct contact liquid cooling (DCLC)solutions from Asetek
>     and CoolIT are much more practical, as are immersion cooling
>     systems using 3M Novec engineered fluid. Novec is really appealing
>     because of the heat transfer efficiency of the change of state. I
>     believe it was originally designed as an electronic parts cleaner,
>     too. It evaporates at room temp like other electronic cleaners, so
>     when you pull hardware out the liquid, it's dry in a matter of
>     seconds, and very clean, too! Much more practical than mineral oil
>     in that regard. 3M claims it has a very low global warming factor,
>     too.
>     Personally, I think DCLC since any leaks in the data center should
>     be smaller than if a tank-like chassis springs a leak, and there
>     one is scared of the environmental impact of water, even when
>     antifreeze and other water treatment chemicals are added to it, as
>     would be needed in this use case.
> 2 phase solutions are sexy but ultimately impractical.
>  * what happens when your recondensing loop fails? and you've 
> evaporated all the fluid off...
I agree that's a problem, but some failures can be mitigated with 
redundancy, like redundant circulating pumps or including the pumps on 
UPS and having proper failsafes incorporated into the cooling system.
>  * try and get a permit to hold large volumes of it in a computer room
>  * try and find a computer room that will allow it in
>  * the above two are mostly due to the low boiling point of the fluid
I understand that. That's why they are usually closed systems.  I would 
like to point out at SC, several booths had open tanks of the stuff on 
the exhibitors floor. I believe IBM says it's safe, but I wouldn't want 
to take my chances breathing it in every day.
>  * expensive (~ an order of magnitude)
> AND you don't actually need a 2 phase solution to get the heat off the 
> cpu's etc.  A single phase solution works just fine.
That's true, which is why water DCLC is a viable option, as well as some 
other thermally conductive liquids that don't rely on boiling (besides 
mineral oil), too, BUT multiphase cooling is much more efficient in 
terms of absorbing/releasing energy.
> -- 
> Dr Stuart Midgley
> sdm900 at sdm900.com <mailto:sdm900 at sdm900.com>

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