[Beowulf] Innovative liquid cooling

[Mark Hahn]

> Though I'm not certain, it seems reasonable to think that the key
> temperature is the junction temperature, which is much higher than
> the air temperature.  With more efficient cooling, that is,

intel/amd spec chips as "Tcase", which makes sense, since they don't
really wanting you removing the heat-spreader.

it's all about delta-T and thermal resistance.  immersion means lower TR, 
so for a given max Tcase (say, 70C), your ultimate heatsink (atmosphere)
can run warmer.  in the video, they were dissipating into the room, which
probably means about 50C.

for an air-cooled system, you need intake temperatures of 15-20C to 
stay under Tcase at normal fan speeds.  hot side will be around 35C,
so it's up to your CRAC to get that back to 15C.

warm-water systems are also based on the idea of reducing TR, so that 
the heat rejection side can run closer to Tcase.  after all, if your 
cluster produces a megawatt of 60C water, that's pretty useful...