[Beowulf] 96 cores in silent and small enclosure

Gerry Creager gerry.creager at tamu.edu
Thu Apr 8 20:06:27 PDT 2010

Prentice Bisbal wrote:
> Lux, Jim (337C) wrote:
>> If you put something  hot into a liquid, you have to worry about forming
>> a film of vapor that keeps the liquid from touching the hot thing, and
>> radically reduces the heat transfer.  It’s all tied up with the
>> turbulence in the liquid, the surface tension of the liquid, etc.
> I'm having flashbacks of my Transport Phenomena class from college.
> Thanks, Jim!

There is treatment available...

>> Boiling is a really good way to move heat: the heat of vaporization is
>> huge, for a small temperature change, 
> Technically, the heat of vaporization occurs at zero temperature change. ;)
>> compared to just the liquid’s
>> specific heat.  But, it’s more complex to design.  It’s used in very
>> high power solid state electronics and in high power vacuum tubes, as
>> well.  The key is that the boiling point of the liquid has to be close
>> to the desired operating temperature of the parts being cooled.  Various
>> Freons work well.
>> Look up Leidenfrost effect (why LN2 droplets skitter around, or water on
>> a hot pancake griddle)..
>> It’s also related to why you can walk across burning coals in bare feet.
>> (the true test of belief in Physics)
> Here's another party trick based on this: Fill a cup (preferably a
> Styrofoam cup for insulation purposes) with liquid nitrogen (LN2) . Then
> stick your finger in it and pull it out real quick. Even though LN2 is
> very cold, you won't fell a thing - the heat from your finger causes the
>   LN2 vaporize before you even contact it, creating an insulating layer
> (film) of nitrogen gas. It's not stable, so if your keep your finger in
> it for longer than a split second, you WILL get freeze your finger!
> Of course, this requires you bringing our own tank of LN2 to the party
> in the first place.

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