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Comment by Paul_Clayton | Hacker News Reader

The enthalpy of vaporization of water (at standard pressure) is listed by Wikipedia[1] as 2.257 kJ/g, so boiling 462 grams would require an additional 1.04 MJ, adding 26 seconds. Cerebras claims a "peak sustained system power of 23kW" for the CS-3 16 Rack Unit system[2], so clearly the power density is lower than for an H100.

[1] https://en.wikipedia.org/wiki/Enthalpy_of_vaporization#Other... [2] https://cerebras.ai/product-system/

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On a tangent: has anyone built an active cooling system which operates in a partial vacuum? At half atmospheric pressure, water boils at around 80 C, which i believe is roughly the operating temperature for a hard-working chip. You could pump water onto the chip, have it vapourise, taking away all that heat, then take the vapour away and condense it at the fan end.

This is how heat pipes work, i believe, but heat pipes aren't pumped, they rely entirely on heat-driven flow. I would have thought there were pumped heat pipes. Are they called something else?

It's also not a refrigerator, because those use a pump to pressurise the coolant in its gas phase, whereas here you would only be pumping the water.

No need to bother with a partial vacuum when ethanol boils at around 80 C as well and doesn't destroy electronics. I'm not aware of any active cooling systems utilizing this though.

I could argue that ethanol has 1/3 the latent heat of vaporization of water, and would boil off 3 times quicker. However, what ultimately matters is the rate of heat transfer, so my nitpick may be irrelevant.

May I introduce you to the glorious vodka cooled PC? https://www.youtube.com/watch?v=IYTJfLyo_vE

I found this review from 2019 of mechanically pumped heat pipe technologies. I skimmed the intro. Looks like it already has a foothold in aerospace.

https://www.sciencedirect.com/science/article/abs/pii/S13594...

> This is how heat pipes work, i believe, but heat pipes aren't pumped, they rely entirely on heat-driven flow. I would have thought there were pumped heat pipes.

Do you have a particular benefit in mind that a pump would help with?

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