2 phase microprocessor cooling system with controlled pool boiling of dielectrics over micro-and-nano structured Integrated Heat Spreaders

Abstract

The present work addresses a microprocessor cooling technique based on pool boiling of a dielectric fluid, HFE-7000 with a compact closed loop thermosyphon, which requires no pumping or auxiliary components to operate. Aiming at modern desktop CPU cooling, the devised system is modular to infer on the optimization of several parameters influencing the system performance. The evaporator bottom surface is enhanced with micro-structured cavities to increase the liquid/solid contact area and optimize nucleation and bubble dynamics within the heterogeneous nucleation process. Optimization of surface structuring must account for several interaction mechanisms and assure that the flow near the surface maximizes the heat transfer mechanisms present in pool boiling heat transfer. This optimization is based on the minimization of steady-state overall thermal resistance of the system and on transient power conditions to control the onset of nucleate boiling and the inherent temperature overshoot upon regime transition at start-up. The condenser tilt angle is optimized as well as the effect of evaporator dimensions, orientation (horizontal and vertical positioning) and liquid fill charges. Based on the outcomes of this exploratory research, a cooling system is implemented in a working computer, cooling a modern CPU, mounted vertically.