Mineral Oil Immersion Cooling: Is it worth it?

in immersioncooling •  2 years ago 


(not my system)

I am building a mineral oil immersion cooling system for my partnered mining project. In the midst of purchasing parts, posting updates among my several social media accounts, and talking with friends, the very first question I hear is usually, "Is that really safe?"

Absolutely. Mineral Oil is a dielectric fluid--meaning that it does not conduct electricity. Provided there are no contaminants that could alter this property (or cause other issues I'll discuss in a moment), this is actually one of the most efficient methods of cooling electronics for the price. There are a lot of mixed feelings floating around about how dangerous mineral oil is to electronics over time, so I thought I'd clear up any misgivings with some science.

So, chemical material reactivity; PCBs (Printed Circuit Boards), excluding those made several decades ago, are comprised mostly of fiberglass, common conductive metals (mostly copper or gold), and epoxy. The chips are mostly silicon infused with other ceramics and low-density conductive metals (think Beryllium). All of these materials have an excellent--if not perfect--chemical resistance to mineral oil.

The I/O components are primarily made up of LCP (Liquid Crystal Polymer--the plastic bits) or a thermoplastic (think Polypropylene or High-Density Polyethylene--which I'll cover shortly), stainless steel, and common conductive metals (again, copper or gold). Again, all of these materials have high chemical resistance to mineral oil.

Even the power cord is wrapped in Polyvinyl Chloride (PVC) which is highly resistant. The most common containers are made of HDPE, PP, or PVC. All of these have good to perfect chemical compatibility ratings. Polypropylene (PP) is perfectly chemically resistant to mineral oil. In fact, it's usually what containers designed to store mineral oil are made of.

Oil contamination can be a problem if you're not careful. Some particulate mass may be conductive and may bridge connections if large enough, and moisture is bad for the same reasons. The simplest and most effective solution to this is installing an oil filter with a fine filter (the filter I use is 99% effective at 10 microns) and a moisture trap or block. In my system, there will be the added benefit of being 100% sealed. The tank has a gasketed lid, and the air is circulated through a HEPA filter--the air in the tank will serve to help cool the oil further.

In short, I am more than confident in the chemical and electrical safety of the subject of this image; So, now let's talk thermodynamics (giddy laughter). The thermal conductivity of air--in terms of humidity, temperature, and atmospheric pressure found in most places you'd build a home--hovers in the 0.02 w/m°k area. Water--mostly pure, common conditions--is 0.6 w/m°k. Mineral oil is 0.133 w/m°k, which isn't as efficient as water but is much better than air.

What this means is that mineral oil will collect the heat faster, AND it will distribute the heat more evenly--meaning any flow is a good flow. Pushing the mineral oil through a radiator and fan to cool it back down before returning it to the tank will serve to cool much faster than with mass air moving over heat sinks.

Now, there is another immersion cooling method that is more efficient called two-phase cooling where the dielectric fluid's boiling temperature is lower than the desired operating temperature of the device. This turns the liquid to its gas state to carry heat away even faster, then it simply cools, condenses on a cooling coil at the top of the sealed tank, and falls back into the oil bath. This way is AWESOME--and thank you, 3M, for giving us Novec fluids--but it's also about 20 times as expensive. I might one day upgrade to two-phase for the sake of experimentation and documentation.

For those interested in immersion cooling, let me start by saying your two best friends are large area, single core radiators and continuous duty (usually 120V) fuel oil transfer pumps. You can--and should--leave the heatsinks and aluminum cases on your miners because the thermal conductivity of aluminum is in the 206 w/m°k area. No heat transfer loss at all. As far as your fans, you have four basic routes; First, you can remove your fans, which is only supported by certain miner firmware. If you cannot remove them, you can try to use them to help circulate the oil, but this will kill the fans over time because of the viscous fluid. Also, some miners will shutdown if the RPMs of the fan do not read what they should. You can snap the blades off of the fans, which is fine if you don't mind having to replace them if you decide to sell the miners. My favorite course of action is to simply suspend the fans above the oil and use them to help keep the tank cooler.

For those of you who think dipping your miners in oil devalues them, remember that this oil is the same oil they use during the machining and cleaning process of manufacturing these devices. Also, the oil will keep the miners free of dust, moisture, and contaminants (providing you're filtering your oil--which is not optional in my opinion).

In summary, mineral oil is safe, relatively cheap, and extremely beneficial to performance. I will certainly be posting pictures, instructions, parts lists, benchmark results, and all other pertinent data as soon as I get everything together.

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