[Beowulf] Re: overclocking with liquids
James.P.Lux at jpl.nasa.gov
Fri Sep 21 15:23:56 PDT 2007
At 07:42 AM 9/21/2007, Peter St. John wrote:
>Thanks all; a couple of people sent me this same article:
>They tried immersion in "ion-free" water (which I would not have
>considered; I thought that since the water molecule is electrically
>asymmetrical, it would always conduct a little...? but I'm not a
>physicist, I just claim to be RGB at book signings) which worked for
>seconds at a time before crashing, apparently no harm to the h/w
>though; then vegetable oil (which they felt looked cool with a
>transparent plexiglass case) which worked better, but still too much
>conductivity for the scale of pins on the CPU. So they sealed the
>CPU, and then all seemed fine. They suggest motor oil would be
>better. Kyle says the latter link is followup, I haven't read that yet.
DI water works for HV equipment.. it's used for cooling high power
vacuum tubes, for instance, but there is always some leakage current.
oil is used to cool all sorts of things (think power distribution
transformers). Vegetable oil spoils: very bad. motor oil has all
sorts of additives. No.. what you want is electrical insulating oil,
such as Shell Diala AX.. low viscosity, clean, designed for the purpose.
The disadvantage of oil? It's a mess if you have to remove the stuff.
What do they use in high dollar gear that really needs
this? Fluorinert, such as FC77. Totally inert, very low viscosity,
doesn't tend to cling to the electronics, etc. available in a variety
of boiling points so you can do "ebullient cooling" (aka 2 phase
cooling)which doesn't need a pump, and is a lot more flow than
straight convective flow. You can also pump and spray it on the
board. It's about a specific gravity of 2.
But.. it's about $500-600/gallon, so don't spill it.
And, it dissolves enough oxygen that rats can be immersed and breathe
it and survive to wiggle another day.
Compared to Diala AX (about $40 for a 5 gallon pail) Fluorinert is in
a different league.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
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