Numerical simulation of gas-liquid transport in porous media using 3D color-gradient lattice Boltzmann method: trapped air and oxygen diffusion coefficient analysis

In non-aqueous Li-air batteries, the liquid electrolytes penetrate the porous media such as carbon nanotube (CNT) paper structure, transport dissolved substances such as oxygen, and play a role in generating reactants on the surface of the porous media. Although the trapped air generated during the electrolyte penetration process could affect the oxygen transport and performance of the battery, this issue has not been sufficiently investigated. Therefore, in this study, the patterns of electrolyte penetration and air entrapment in porous media were investigated through numerical analysis. A multi-relaxation time color-gradient lattice Boltzmann method was employed for modeling. Based on a two-phase flow simulation in porous media, electrolyte penetration and trapped-air saturation were analyzed in terms of porosity, wettability, and viscosity ratio. The porosity and viscosity ratio did not considerably affect the trapped-air saturation, whereas wettability had a significant effect on the aforementioned parameter. In addition, for each variable, an increase in the effective diffusive coefficient corresponded to increased porosity and hydrophilicity, as well as an improved viscosity ratio.