We've been working behind closed doors for a long time, but only recently we have been asked to come out and prepare a couple of presentations about the advantages and benefits of passive 2-phase immersion cooling, and why it is so elegant and efficient. One of them, a simple poster, will be used at the Supercomputing Conference (27th Annual HPCC Conference) in Rhode Island, USA, March 26-28th 2013.
Immersion cooling has been around for a long time. The physical heat transfer properties of immersion cooling are nothing new. We all know a few things about physics, such as that water usually boils at around 100°C, that at the top of a mountain it probably boils at a little lower temperature due to the reduced pressure at altitude. We also know that when we sweat in the summer heat, the evaporation process on our skin "somehow" helps us to cool down. It's the same principle that applies to 2-phase immersion cooling aka evaporative immersion cooling.
The short and simplified story is, when the liquid changes to gas or vapor (phase change taking place) at the hot surface of electronics, the gas molecules take a lot of heat energy away with them. The same thing happens when you cook your pasta. Energy, in form of heat from the hot part of the stove, rises with the steam and "disappears". Now, try the same with oil and you'll see the heat will probably stay where it is: in your pot and in your oil. No evaporation, very little heat transfer.
And this is basically exactly what the military and aerospace companies have been doing for a long time. You can read all about Thermal Management Fluids from 3M and Military and Aerospace Applications here. As you can imagine, the military has many mission critical applications and they definitely have means to put a couple of bright engineers in a room and build a sealed box that contains the latest and greatest in military tech. And they don't mind it being closed and sealed, since it will protect the valuable gear from dust and debris in a helicopter or a Humvee in the middle of the desert. But for us mortal beings, that's certainly not how we would want our valuable server or computational cluster to run. We certainly wouldn't want it under pressure, not in a sealed box, and probably also not boiling away at 100°C (ever wondered why military spec Xilinx FPGAs have a maximum junction temperature of 125°C, while everybody else has to live with 85°C?).
So, it's no surprise that some of the first questions we often get when talking about the technology is, "how much does it cost?" and "isn't that very complicated?". Military projects have a lot of money to burn and so do companies with big airplanes. We get surprised faces when we mention that it is actually cheaper to buy, build and run, than air conditions, fans and all the overhead that comes with it.
The reason lies within a very simple concept called Open Bath Immersion Cooling and cleverly designed liquids with relatively low boiling points (ie. 3M Novec Engineered Fluids). Take Novec 649 for example, it boils at a comfortable 49°C, or Novec 7100 at 69°C. That's just warm to touch and keeps your electronics relatively cool compared to a fan which is struggling to get the heat out (until your mainboard/BIOS throttles down the CPU or kicks in the fan's next gear). There's even a fluid (Novec 7000) that boils at 34°C, which is cooler than your body temperature. In fact, forget about throttling, fans, even temperature sensors. With immersion cooling and liquids that boil at 49°C, your hardware just won't get warmer than that - it stays nice and comfortable and all the heat is taken away by the rising vapor passively without a single fan and spending extra energy and space.
Anyways, to cut this long story short, we have started to spread the word and introduce a handful of people to our simple concepts of passive 2-phase immersion cooling. Here are a few first documents that you might find interesting. There will definitely be more in the near future, so you won't be running out of reading material anytime soon.
We have also started to create a publications section on the web site. That's where we will be linking to information around immersion cooling and its uses.
If you want to learn more about immersion cooling and how it works, including a graphical description of the passive 2-phase immersion cooling cycle, please click the following link:
March 26-28th 2013.
I am glad you posted that. Testing.