Modeling and Testing of an Integrated Evaporator-Condenser Device for CPU Cooling

CPUs with high clock rates can dramatically increase heat dissipation within their encapsulation due to internal Joule heat from the transistors. The conventionally used air cooling systems for CPUs, such as the aluminum or copper extruded heat sink types, have severe heat transfer “bottlenecks” due to high thermal resistances and they easily reach their thermal design limits (TDL). Alternative cooling devices such as heat pipes and liquid cooling tends to have externally attached radiator/condenser and/or pump and such designs are cumbersome. This paper describes the modeling, design, and testing of a compact (about the size of the Intel stock cooler, diameter: 96mm, height: 50mm), fully integrated, orientation-free, evaporator-condenser device for CPU cooling, with excellent attributes of low thermal resistance from phase change phenomena and minimal vapor pressure drop. The prototype fabricated is designed to reject 200 W (twice the capacity of conventional heat sinks). It is made of copper and uses distilled water as the working fluid. The working fluid boils inside a porous structure clad evaporator and is transported radially to nearby air-cooled condenser sections; this unique arrangement minimizes space while providing adequate area for air convection. Testing was done by subjecting it to varying heat loads and air flow rates. A best performance of 0.206 K/W of the device’s thermal resistance was achieved at a fan air flow rate of 34.5 CFM under 203 W of cooling load, and moreover, these results are in good agreement with the simulation. Further improvement of the current design could yield significantly better performance as the device has yet to reach its full potential, especially with regard to the design of its air-cooled curvilinear fins and boiling enhancement.