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

This article reports the results of our numerical studies on the performance of thin-film evaporation, mostly seen in the evaporator of a thin vapor chamber, using micropillar arrays of varying pitch and under both uniform and nonuniform heat flux conditions. The dry-out heat flux and evaporator surface temperature have been used as 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 a variable pitch of the micropillar array and with both uniform and nonuniform heat flux at the base. The pitch variations are done either by maintaining the mean pitch to be constant (the 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 (+x-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 an increase in cooling limit is accompanied with an increase in overall evaporator surface temperature. In addition, the interplay of variable spacing and nonuniform 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, thus recommending more pillars in high heat flux zones.