It's possible it never made it into production; but when I was helping to commission a 4 rack "supercomputer" circa 2010 we used APC's in-row cooling (which did glycol exchange to the outside but still maintains the hot/cold aisle) and I distinctly remember reading a whitepaper about racks with built in water cooling and the problems with pressure loss, dripless connectors, and corrosion. I no longer recall if the direct cooling loop exited the building or just cycled in the rack to an adjacent secondary heat exchanger. (And I don't remember if it was an APC whitepaper or some other integrator.)
There's also all the fun experiments with dunking the whole server into oil, but I'll give you that again I've only seen setups described with secondary cooling loops - probably because of corrosion and wanting to avoid contaminants.
There's also all the fun experiments with dunking the whole server into oil, but I'll give you that again I've only seen setups described with secondary cooling loops - probably because of corrosion and wanting to avoid contaminants.