See https://www.anandtech.com/show/12522 for the full story.
Big data centers are often cooled by air, and large HVAC/air-conditioning machines. The ones near the Arctic Circle can rely on the outside air to help. If a center invests properly, especially with a specific design and layout in mind, then using water cooling is another investment that can be made. If a designer really wants to go off the deep end, then full immersion liquid cooling is a possibility.
Immersive liquid cooling is ultimately not that new, and is based on non-conductive liquids. It allows for the full system to be cooled: all of the components, all of the time, and removes the need for large cooling apparatus, and encourages energy recycling, which is a major metric for data center owners. For data centers limited by space, it also offers better density of server nodes in a confined space, ideal for deployments on the edge of communication networks.
There are two angles to immersion cooling: non-phase change, or phase change. The first one, non-phase change, involves using a liquid with a high heat capacity, and cycling through a heat exchange system. The downside of those liquids is that they often have a high viscosity (mineral oil), requiring a lot of energy to forcibly circulate. By contrast, the phase-change variety is, for most purposes, self-convecting.
The idea here is that the liquid being used changes from a liquid to a gas by the act of being warmed up by the component. The gas then rises up to a cool surface (like a cold radiator), condenses, and then falls, as it is now cooler again. The energy transferred into the radiator can then be circled into an energy recovery system. The low viscosity of the phase change material aids significantly in the convection, with the act of creating a large volume low density gas displacing the liquid for that convection.