Capillary Wicking and Permeability in Random Particulate Porous Media: A Physically Scaled Pore-Scale Simulation

Abstract

Random particulate porous media are widely used as capillary wicks in heat pipes and vapor chambers, where fluid transport is governed by the permeability and capillary wicking dynamics. In this work, we perform three-dimensional (3D) lattice Boltzmann simulations to investigate microstructure-regulated permeability and capillary wicking dynamics in random particulate porous media. Crucially, to overcome a prevalent limitation in the existing literature, where reliance on dimensionless parameters obscures the actual physical scale, we establish a rigorous unit conversion method that maps lattice quantities directly to real-world physical dimensions. This enables high-fidelity direct evaluation and quantitative prediction of transport phenomena within micrometer-scale porous media. The conversion is further extended to a water-air two-component system, which allows the simulated capillary transport process to be related to more common liquid-air environments in natural and engineering porous media. Various structural configurations, including overlapping, independent, and ellipsoidal particles, are generated to comprehensively examine the effects of the porosity, particle diameter, size dispersion, packing mode, and particle shape. Results indicate that permeability increases approximately exponentially with porosity and exhibits a square law dependence on particle diameter. At a fixed porosity and base particle diameter, particle size dispersion reduces the permeability, accompanied by an increased specific surface area and a decreased average local throat diameter. Spontaneous capillary wicking simulation results show that the wicking rate varies nonmonotonically with porosity, and the maximum capillary rise coefficient appears at an intermediate porosity. By combining the steady-state permeability and dynamic wicking simulation results through the Darcy–Washburn pressure balance, we obtain the effective capillary pressure and apparent capillary performance coefficient. This study provides a rigorous, physically scaled pore-scale approach for evaluating capillary-driven liquid transport in random particulate porous media.