Direct-to-chip liquid cooling (cold plates)
Beginner
Cooling a chip with water that flows through a metal block pressed right on top of it.
Novice
Metal cold plates with tiny internal channels sit on the hottest chips in place of air heat sinks. Water or a water-glycol mix pumps through them and carries the heat out of the rack. Other parts still need some air cooling.
Expert
Single-phase water/propylene-glycol loops (the technology cooling system) fed by a CDU; two-phase refrigerant versions exist. Captures most but not all rack heat, so residual air cooling is still needed. Enables warm supply water (ASHRAE W32–W45) and dry coolers, but needs tight control of chemistry, filtration and flow.
Explained in Power and cooling (Systems).
See also: CDU (coolant distribution unit), Immersion cooling, Rear-door heat exchanger.