With the exception of some uncommon specialized hardware systems (and, surprising to many, laptops), there are for practical purposes few “liquid-cooled” hardware used in commercial data centers today. The definition of liquid-cooled hardware is where the primary heat transfer medium inside the hardware itself is a liquid that exists internally within the electronics. Some super-computers and old legacy mainframes employ liquids that are piped directly into the hardware to cool the heat generating electronics. There are also some specialized military electronic packages that use evaporative spray-cooling technologies and some computer game manufacturers that utilize true liquid cooling designs.
Many of the liquid cooling solutions hitting today’s market still require air-to-liquid heat exchangers that provide air cooling at the individual rack where the electronic equipment is housed. The IT hardware chassis include integral fans to move the cool air through the inside of the hardware chassis to move the heat from the electronics to the air within the cabinet (or rack). Technically, this is still air cooled hardware.