Role of Interfacial Evaporation Process in Thin Vapor Chambers With Variable Pillar Spacing and Nonuniform Heat Flux

Abstract

This paper reports the results of our numerical studies on the performance of thin film evaporation, mostly seen in the evaporator of a thin vapour chamber, using micropillar arrays of varying pitch and under both uniform and non-uniform heat flux conditions. The dry-out heat flux and evaporator surface temperature have been used as the performance metrics. A numerical model has been formulated to solve the fluid flow and phase change heat transfer considering the capillary pumping action (wicking action). The model is next exercised to study the performance of the evaporator with variable pitch of the micropillar array and with both uniform and non-uniform heat flux at the base. The pitch variations are done either by maintaining the mean pitch to be constant (same number of pillars) or by keeping the limiting pitch (maximum) equal to the uniform pitch scenario. The results show that a linearly decreasing pillar spacing arrangement along the downstream direction, i.e., along the flow direction (+ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> direction), results in significant enhancement of the cooling limit up to 1.5 times along with the reduction in overall evaporator surface temperature when compared to uniform pillar spacing where increase in cooling limit is accompanied with increase in overall evaporator surface temperature. In addition, the interplay of variable spacing and non-uniform heat flux results in design guidelines for pillar arrangements for given power maps while throwing new insights into the complex fluid flow and heat transfer phenomena encountered in this process. A higher concentration of pillars is found to result in lower evaporator surface temperatures, thereby recommending more number of pillars in high heat flux zones.