New Approach To Immersion Cooling Powers HPC In a High Rise

miller60 writes "How do you cool a high-density server installation inside a high rise in Hong Kong? You dunk the servers, immersing them in fluid to create an extremely efficient HPC environment in a hot, humid location. Hong Kong's Allied Control developed its immersion cooling solution using a technique called open bath immersion (OBI), which uses 3M's Novec fluid. OBI is an example of passive two-phase cooling, which uses a boiling liquid to remove heat from a surface and then condenses the liquid for reuse, all without a pump. It's a slightly different approach to immersion cooling than the Green Revolution technique being tested by Intel and deployed at scale by energy companies. Other players in immersion cooling include Iceotope and Hardcore (now LiquidCool)."

Two phase is asking for trouble.

[camperdave]

Using a boiling liquid is asking for trouble. True, a phase change like boiling can conduct away a lot of heat, but there are other issues. First of all, vapour does not conduct as much heat as liquid, so there's going to be an insulating layer of vapour over all of the components that need it most. It's called the Leidenfrost Effect [wikipedia.org]. Second, bubbles expanding and collapsing causes an effect called cavitation, which can erode components. It is a constant sonic vibration which can induce metal fatigue in delicate wires (such as the leads inside a chip), and can cause cracks in inflexible materials such as silicon chips and ceramics (capacitors and resistors).

Re:Two phase is asking for trouble.

[sugarmatic]

Nucleate boiling is what keeps the lights on if you depend on coal or gas for your electricity. It precedes the zone where your Leidenfrost effect is relevant, and actually increases the heat transfer coefficient by factors.

Tuning a closed system to exploit this is an exercise (fluid chemistry, pressure, temperature), but it is also ubiquitous. As for cavitation, it's a red herring in the nucleate boiling zone- the size of the bubbles is so small, and hence the driving frequency is so high, there is a) less mechanical coupling for the vibration, and b) the energy of cavitation is so low as to not be an issue.