Thermal control of high-powered desktop and laptop microprocessors using Two-Phase and Single-Phase loop cooling systems

The development of high-end and compact computers has resulted in a considerable rise in the power dissipation requirements of their microprocessors. At present, the waste heat release by the Central Processing Unit (CPU) of a desktop and server computer is 80 to 130 W and a notebook computer is 25 to 50 W. New systems have already been built with thermal outputs as high as 200 W for desktops and around 70 W for laptops. At the same time, the heating areas of the chipsets have become as small as 1 to 4 cm2. This problem is further complicated by both the limited available space and the restriction to maintain the chip surface temperature below 100 ºC. It is expected that conventional two phase technologies like heat pipes and vapour chambers as well as current designs of single phase cooling systems will not be able to meet these future thermal needs of computer systems. With the intention of finding a solution to this problem, different thermal designs based on both two-phase and single-phase heat transfer were developed and characterized for the thermal control of high density microprocessors. In the domain of two phase technology, two investigative prototypes of capillary driven passively operating loop heat pipes with characteristic thickness as small as 5 or 10 mm and capable of dissipating heat fluxes as high as 70 W/cm2 were designed and tested.<br><br> These devices responded very well to the thermal needs of laptop microprocessors. The thermal characteristics of single phase cooling systems were enhanced with the purpose of handling concentrated heat fluxes as high as 400 W/cm2. This was made possible by developing heat sinks with innovative microstructures that include microchannels or sintered microporous media. As an outcome of the present research work, it is concluded that two phase cooling units provide a highly reliable thermal solution for the cooling of laptop microprocessors with high heat fluxes and limited available space for accommodating thermal devices. However the thermal performance of the passive devices is limited at very high magnitudes of heat flux. Therefore cooling technology needs to be further explored for the effective management of future high powered electronic systems. Liquid cooling systems can handle extremely high heat fluxes very effectively but they are structurally complex and unreliable due to the requirement for an active component (like a pump) in the system that also requires power for its operation.