Why would you use oil as the liquid though? Why not water? It's free, and has better heat capacitance.
I don't understand why people can't spend 30 seconds on Google to answer their question. I found a great article about how oil is perfect for cooling off circuit boards.
https://www.nsa.gov/research/tnw/tnw202/article4.shtmlIn summary it says:
Unfortunately, we cannot dunk a computer in water like a burnt finger since electricity and water do not play well together. Mineral oil, on the other hand, has been used by electric utilities to cool electrical power distribution equipment, such as transformers and circuit breakers, for over 100 years. Mineral oil only has about 40% of the heat holding capacity and about one quarter the thermal conductivity of water, but it has one huge advantage over water—it is an electrical insulator. This means that electrical devices can operate while submerged in oil without shorting out.
While mineral oil does not have the heat capacity of water, it still holds over 1,000 times more heat than air. This means that the server rack discussed earlier that needed 1,200 CFM of air to keep from burning up could be kept cool with just about 1 CFM of oil. The energy required to pump 1 CFM of oil is dramatically less than the energy required to blow 1,200 CFM of air. In a perfectly designed data center, where the amount of air blown or oil pumped is matched exactly to the heat load, the energy required to blow air is five times that required to pump oil for the same amount of heat removed. In reality, the amount of air moved through a data center is far more than that required to satisfy the load. This is due to the fact that not all of the air blown into a data center passes through a computer before it returns to the CRAC unit. Since the air is not ducted directly to the computers' air intakes, it is free to find its own path back to the CRAC unit, which is frequently over, around, or otherwise not through a server rack. As we will soon see, it is much easier to direct the path of oil and to pump just the right amount of oil to satisfy a given computer heat load. Thus, the energy required to circulate oil can be more than 10 times less than the energy required to circulate air.