UC Irvine

The continually increasing power density of high-performance electronics is bottlenecked by the challenges faced with thermal management requirements for reliable operation. While the traditional convective air-cooling approach is limited in its effectiveness at dissipating high heat fluxes, the use of latent heat in liquid-vapor phase change is an attractive strategy for managing the most aggressive thermal loading demands. Passive two-phase cooling operates by capillary pumping fluid through void spaces within porous metals to transport energy over long distances. The performance of such liquid delivery through porous structures is governed by the pore distribution, porosity, and morphology. Analogous to energy transport in polycrystalline solids, hydraulic transport in polycrystalline porous media is also limited by structural defects and grain boundaries. This work reports on the capillary performances of both single- and polycrystalline microporous copper with varying pore diameters from 300 to 1000 nm. The hydraulic transport through the arrays of interconnected spherical pores is modeled and quantified with experimental wicking measurements, and the influence of grain boundaries on the hydraulic transport in polycrystalline microporous media contributes to the hydraulic resistance presented by the structural defects. By combining multiple pore diameters and systematically layering them, this study creates heterogeneous

porous media to emulate the transport within biological systems. The gradient layering of pores enhances the liquid delivery by circumventing grain boundary defects in three dimensions. The fundamental understanding of hydraulic transport physics through porous crystals and boundaries will pave the way for the spatial design of heterogeneous porous materials for future capillary-driven technologies.