Advanced technology for server cooling

This paper reports work on advanced cooling technology for servers. The air cooling load on the rack may be enhanced using highly compact Copper/Brass "flat tube" water-cooled heat exchangers that are integrated into the rack frame. The cooling water is supplied by a water chiller. Analysis shows that it is possible to provide cooling (UA/A(fr)) in the range of 670-1000 W/m(2)-K, where the m(2) is the core frontal area. Also analyzed and compared are advanced technology CPU heat sinks - a thermo-syphon concept and a liquid micro-channel heat sink. The thermo-syphon may be used in a compact thermal-bus concept for heat removal from multiple CPUs. Used with boiling on an enhanced copper boiling surface in a thermo-syphon, heat loads in excess of 75 W/m(2)-K are possible. The heat removed at each CPU in the chassis is rejected to water flow in a compact water cooled condenser. Performance results of the thermo-syphon concept are predicted, obstacles associated with increasing performance are discussed, and possible solutions are proposed. Performance predictions were also made for water cooled: (1) Copper microchannels as an attached external sink and (2) Silicon microchannels integral to the silicon CPU die. It is shown that microchannels integrated into the silicon die do not offer significant advantage over copper micro-channels.