Transport phenomena in high porosity fibrous metal foams.

摘要

The primary goal of this thesis is to investigate the transport phenomena that arise in high porosity ({dollar}>{dollar}0.85) metal foams. An important application of metal foams is in the cooling of electronic packages. This bias is reflected in the research conducted. Metal foams made of aluminum with porosities ranging from 0.89-0.97 and poresizes in the range 5-40 PPI (pores per inch) are used.; Due to the complexity of the physical structure, the method of volume averaging is employed to formulate the governing equations. This involves averaging the constitutive equations for plain media over representative elementary volumes (REVs). While this approach successfully simplifies the general problem, information about the transport occuring in the length scale of the REVs (microtransport) and, more importantly, its effect on the overall macro transport is needed. Studies have been conducted, in a systematic manner, to quantify the microtransport and relate it to the relevant parameters that describe the structure of the metal foam matrix.; The stagnant thermal conductivity, {dollar}ksb{lcub}e{rcub},{dollar} is measured experimentally and an analytical model is developed, based on the metal foam structure. The permeability, K, and the inertia coefficient, f are measured experimentally, and their values are related to the metal foam structure through an empirical model. The thermal dispersion conductivity, {dollar}ksb{lcub}d{rcub}{dollar} is determined by numerical modeling using experimentally measured heat transfer rates. The numerical predictions are made without invoking the assumption of local thermal equilibrium. For this purpose, it is necessary to model energy transport in the solid and fluid phases separately.; As a prelude to using metal foams for electronics cooling of a flip-chip package, the cooling configuration is studied in order to benchmark the base case, i.e. without the heat sink. To this end, a numerical study of mixed convection in a partially open vertical enclosure is performed. Two kinds of analyses (symmetric and full domain) are investigated for two values of the Grashof number {dollar}(10sp4, 10sp5).{dollar} For {dollar}Gr=10sp4,{dollar} both the analyses yield identical results. However, for {dollar}Gr=10sp5{dollar} hysteresis is observed for the symmetric domain analysis only. For the full domain analysis, asymmetric solutions, similar to the kind observed experimentally in similar configurations (e.g. Vapor Phase Epitaxy), are obtained. The variation of the Nusselt number as a function of the mixed convection parameter, {dollar}Gr/Resp2,{dollar} is plotted and discussed.; Finally, the application of metal foams to electronics cooling is explored. A novel finned metal foam heat sink is proposed and its performance is evaluated. The impact of the present work, and possible extensions are noted.