As somebody that worked on Google data centers after coming from a high performance computing world I can categorically say that Google is not “re-learning” old technology. In the early days (when I was there) they focused heavily on moving from thinking of computers to thinking of compute units. This is where containers and self contained data centers came from. This was actually a joke inside of Google because it failed but was copied by all the other vendors for years after Google had given up on it. They then moved to stop thinking about cooling as something that happens within a server case to something that happens to a whole facility. This was the first major leap forward where they moved from cooling the facility and pushing conditioned air in to cooling the air immediately behind the server.
Liquid cooling at Google scale is different than mainframes as well. Mainframes needed to move heat from the core out to the edges of the server where traditional data center cooling would transfer it away to be conditioned. Google liquid cooling is moving the heat completely outside of the building while it’s still liquid. That’s never been done before as far as I am aware. Not at this scale at least.
Liquid cooling at Google scale is different than mainframes as well. Mainframes needed to move heat from the core out to the edges of the server where traditional data center cooling would transfer it away to be conditioned. Google liquid cooling is moving the heat completely outside of the building while it’s still liquid. That’s never been done before as far as I am aware. Not at this scale at least.