EMBEDDED TWO-PHASE COOLING OF HIGH FLUX ELECTRONICS VIA MICRO-ENABLED SURFACES AND FLUID DELIVERY SYSTEM (FEEDS)

Abstract

A novel cooler utilizing thin Film Evaporation on micro-Enabled surfaces and fluid Delivery System (FEEDS) is embedded into silicon die with the goal of achieving the metrics proposed by the Defense Advanced Research Project Agency’s (DARPA) ICECool fundamentals program: a heat flux of 1 kW/cm2 at superheats below 30 K, vapor qualities above 90%, pressure drops below 10% of absolute pressure, and heat densities of 1 kW/cm3. Preliminary models were used to investigate the various physical phenomena affecting two-phase flow in manifold-microchannels, including nucleate boiling, flow regime, annular film evaporation, void fraction, single-phase fully developed and developing forced convection, intra-microchannel flow distribution, and fin conduction. The various physical phenomena were then combined into a novel “2.5-D” microchannel model, which uses boundary layer assumptions and simplifications to model the 3-D domain with a 2-D mesh. The custom-coded microchannel model was first validated by comparing single-phase thermal and hydrodynamic performance to a 3-D laminar flow simulation performed in ANSYS Fluent with errors of less than 5% as long as the flow remains two-dimensional. Two-phase validation was conducted by comparing past experimental data to model predictions, and found to provide heat transfer predictions that were qualitatively accurate and correct in order of magnitude, and pressure drop predictions accurate to within 30%. A parametric study was then performed in order to arrive at a baseline geometry for meeting the ICECool metrics.

A system level model was created to select the working fluid, and a manifold model was created to evaluate manifold flow configuration. A novel flow configuration capable of providing an even inter-microchannel flow distribution in two-phase mode was proposed, and a working manifold designed for the baseline geometry. Experiments with a press-fit FEEDS chip were then conducted, obtaining heat fluxes in excess of 1 kW/cm2 at 45% vapor quality. The volume of the FEEDS assembly was then reduced by bonding a chip directly to a FEEDS manifold. A bonding apparatus capable of providing a uniform and conformal clamping force was designed, fabricated, and used to hermetically bond the manifold to the chip. Three bonded chips were then tested, obtaining a maximum heat flux of 700 W/cm2 at vapor qualities approaching 30% and a heat density of 220 W/cm3.