Fabrication And Characterization Of Aluminum Vapor Chamber Using Micro-grooved Wick With Reentrant Cavity Array

Micro-grooved wick with reentrant cavity array(MGRA)was developed in order to enhance the heat transfer performance of ultra-thin aluminum vapor chambers.Using the orthogonal ploughing/extrusion(P/E)method,high aspect-ratio micro-grooves and reentrant cavity array were obtained on a thin substrate with a small cutting depth,which yielded both high capillary and boiling limit.The experimental results indicated that the MGRA vapor chamber had favorable heat transfer performance.The highlights of this paper are as follows:(1)Manufacturing and characterization of MGRAA ploughing/extrusion(P/E)tool for planning was designed.The MGRA was produced using the the orthogonal ploughing/extrusion method.The plastic metal flow and the mechanism of the formation of reentrant cavity array were analysized.In order to optimize the structural design of the MGRA,the relationship between the P/E paramters and cavity structure was discussed.With the assistance of FEM simulation operated on Deform,the metal flow field as well as the effective stress distribution during the P/E process were obtained,which helped identify the critical step during the formation of the micro-groove and reentrant cavity.(2)Characterization of capillary limit for MGRAThe capillary rise height and rising rate for the MGRA were invesitigated using the IR-thermal imaging method,which revealed that the capillary valve effect of the reentrant cavity enhanced the capillary performance of the MGRA.In addition,the pressure drop and permeability of the wick were studied using the forced flow method.A comprehensive evaluation factor K·?Pcap was established based on the capillary limited heat flux in order to compare the capillary limit between the MGRA and MG.The comparative study identified the positive effect of the reentrant cavity array on the capillary limit of the wick.Further study on the effect of structural parameters on the capillary rise,permeability and K·?Pcap was conducted for structural optimization of the MGRA.(3)Characterization of boiling limit for MGRAThe onset of nucleat boiling(ONB),two-phase heat transfer coefficient(HTC)as well as critical heat flux(CHF)for the MGRA during pool boiling were investigated,which justified the enhancement of start-up performance and boiling limit using the MGRA for the Al-vapor chamber.With the assistance of high-speed visualization,the bubble nucleation mechanism and bubble departure diameter for both the micro-groove and reentrant cavity on the MGRA were studied.Besides,the relationship between the bubble dynamics and two-phase heat transfer performance was analysized.(4)Thermal response characteristics of MGRA vapor chamberThe start-up performance,thermal resistance at steady state and heat transfer limit of the MGRA vapor chamber were investigated.In addition,the effect of operational orientation and cooling power on performance of the vapor chamber were also studied.The MGRA vapor chamber was compared with other designs in literatures in order to justify its competitive heat transfer performance.