On 3/24/24 2:38 PM, Michael DiDomenico wrote:
i'm curious if others think DLC might hit a power limit sooner or later, like Air cooling already has, given chips keep climbing in watts.
I've heard different numbers over the years, but water is something like 3000x more effective as a cooling fluid than air. This is why water can be a much higher temperature going into the rack than air. A much smaller temperature difference is needed for the same heat transfer rate.
So processors can produce a lot more heat than they are now before we hit the same issue we're currently seeing with air. I don't think processors will ever get near that limit. I think other issues would keep them from getting there, like they stop working due to the high internal temps.
If we do start to hit limits with liquid cooling, either DLC or immersion, there's two knobs we can twist to help us: Increase flowrate and and decrease inlet temperature both of those will increase cooling capacity. Because a of the high thermal capacity and conductivity of water, a small temperature change can make a huge difference in heat transfer rates compared to air.
With air, we can't really do too much to practically increase flowrate. The flowrate through the chassis is dictated by two things: The resistance to flow through the chassis, and the pressure drop across the server. We can't do too much from a practical point of view to increase the pressure drop. We can't really create a significant vacuum in the hot aisle, nor can we create too much pressure on the inlet side. Neither situation really works in a data center that humans have to work in, and move into and out of regularly. And since air is compressible, as we increase the inlet pressure, it compresses and heats up... yadda, yadda, yadda... Hot aisle and cold aisle containment and a few more fans is about the best we can do practically to reduce mixing and maximize airflow through the racks. Of course, as you add more fans, your PUE goes down.
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