[Beowulf] Innovative liquid cooling

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Fri Mar 1 14:30:49 PST 2013


On 3/1/13 11:00 AM, "Mark Hahn" <hahn at mcmaster.ca> wrote:

>> For future reference, I just looked up these thermal conductivities:
>>
>> Air : 0.024 W/m-k (at 298K)
>> Water:  0.58 W/m-k (at 300K)
>> Mineral oil: 0.162 W/m-k
>> 3M Novec 7000:  0.075 W/m-k
>
>H2 is 0.168 at 25C.  *that* is what we should all be cooling our clusters
>with!
>

There's a lot more than just the thermal conductivity. There's also the
specific heat and the viscosity..

Thermal conductivity affects how the heat "propagates" into the coolant,
but, for instance, the specific heat sets how much it changes temperature
for a given amount of heat.

Then you have the density and viscosity, which also affect temperature
rise and pumping effort/speed.

I'm curious about why Novec 7000
"Novec 7000 fluid is pumpable to -120 deg C; is nonflammable; and is not
regulated for transport or use. This product is used in a diverse range
of industries. Its unique properties make it useful as a low
temperature, heat transfer medium and as a refrigerant."

It has low global warming potential, but then, so does mineral oil.  In
this application, the "pumpable to -120C" isn't particularly useful.  I
wonder if it's a stock bottle photo? It also boils at 34C, so you could
almost boil it in your hands.

Novec 7100 boils at 61C, which is a bit low if you're cooling things with
case temps of 70C.. You don't want bubbles insulating you from the coolant.
There's a whole bunch of other Novec 7x00 fluids with Bps up to 131C


I do note that high power turboalternators are cooled with hydrogen: very
good conductivity and also very low viscosity and density, so "windage
loss" is lower.

>



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