Thermophysical Properties of Monoporous Sintered Copper

Abstract

Thermophysical properties of monodispersed-sintered copper are measured. An apparatus to measure effective thermal conductivity of dry and wet samples is built. It is calibrated using bulk samples with known thermal conductivity. Permeability is measured based on flow resistance though the porous samples. Velocity at different pressure drops is measured and the permeability calculated using Darcy’s law. The experiment is performed using water and silicone oil as working liquids. The error of the measurement is less then five percent. Capillary pressure for all samples is measured based on amount of liquid that is held by the porous sample. The Young-Laplace relationship is used to relate capillary pressure to effective pore radius. Porosity of the samples is calculated by measuring the dimension of samples and weighing the amount of liquid in fully saturated samples. Thermal conductivity and capillary pressure are found to decrease as powder diameter increases; permeability and porosity increases with powder diameter.

Recent Advances in Vapor Chamber Transport Characterization for High-Heat-Flux Applications

“…Atabaki and Baliga [124] reviewed several thermal conductivity models for two-phase mixtures and developed a modified empirical correlation based on experimental data for sintered metal powders [123,124]. Similar testing of biporous and monoporous sintered copper powders performed by Catton and coworkers [64,125] revealed that the effective medium theory model [126] discussed by Carson et al [127], which assumes a random dispersion of both material phases, provides an upper bound on effective thermal conductivity. Li and Peterson [128] reviewed models for predicting the effective conductivity of layers of wire screen, and performed experiments using sintered screen to validate a proposed analytical model as a function of the mesh number and wire diameter.…”

“…An empirical correlation for permeability was developed, and geometries were identified for which accuracy was improved compared to the modified Blake-Kozeny equation [1]. A number of additional comparisons have been drawn against the Carmen-Kozeny theory based on experimental measurement of felt [133], metal screen [134], sintered powder [125], and composite [135] wick permeability.…”

“…In the bubble-point method [136], the capillary pressure is determined based on the minimum pressure required to penetrate gas through the sample; a bubble will first pass through the largest pore, providing a conservative estimate. Conversely, the maximum capillary pressure can be determined by measuring the pressure head sustained by a plug of wick material holding a liquid column against gravity [64,125,137]. An alternative method is to measure the transient rate of rise of liquid in a sample to predict the capillary pressure and permeability based on Washburn's equation [138], as first described with respect to heat pipe wick materials by Adkins and Dykhuizen [132].…”

Evaporation analysis in sintered wick microstructures

“…One such method known as the bubble-point method provides a conservative estimate of capillary pressure [37]. On the other hand, the maximum capillary pressure provided by the wick structure may be determined by measuring the gravitational head needed to break the liquid column in a plug of wick material saturated with liquid [38,39]. Another technique, known as the rate of rise test, observes the transient rise of liquid in a sample for estimating the effective pore radius, and has been widely used [37,40].…”

Thermal Resistance Measurement across a Wick Structure Using a Novel Thermosyphon Test Chamber

“…Lin et al [1,2] measured the thermal conductivity of saturated mono-porous and bi-porous sintered copper, but did not include phase change effects. Cao et al [3] compared mono-dispersed and bi-dispersed copper wicks and illustrated the benefit of using two characteristic pore sizes to optimize both permeability and capillary pumping pressure.…”