Lattice Boltzmann simulations for invasion patterns during drying of capillary porous media

Drying of capillary porous media involves coupled heat and mass transfer in complex void space geometry, which makes it very difficult to model and simulate invasion patterns. Thus far, modeling of drying was done using either continuum methods or pore network models (PNM), both of which have some limitations on representing the geometry of void space and underlying transport mechanism. Pore network models were in general applied to reconstructed void space, therefore, dynamic invasion patterns, cluster formations and dependency on drying kinetics may not be accurate. Alternatively, Lattice Boltzmann Method (LBM) is ideal for simulation of drying in capillary porous media as it can incorporate complex effects in a simple and natural way. In this work, the Lattice Boltzmann Method (LBM) using Shan Chen multiphase representation is used to simulate invasion patterns during the drying of four different void space computation domains, differing in both pore and throat geometries. The dynamics of invasion patterns and cluster formation were captured in all four computation domains. Due to the complex geometries present in porous media, capillary instabilities are often observed which leads to sudden jumps in the fluid-fluid interface. In this work, the effects of such instabilities on the liquid distribution are studied. The invasion patterns are compared to identify the dependence of capillary instabilities on the pore structure. It was observed that fluid-fluid interface motion could be classified into two types- evaporation-diffusion invasion, which constituted of slow invasion of voids by diffusion, and Haines jumps, which involved fast invasion of voids due to capillary instabilities. It was observed that some types of porous media exhibited an abundance of the former, particularly in irregular pore structures. However, regular pore structures showed a combination of both evaporation-diffusion invasions and Haines jumps. Lastly, it was observed that the rate of invasion of pores depends on its structure. Pores with sharp edges take a considerably longer period to invade due to a liquid holdup at the edges. This work emphasizes the advantages of using the LBM to simulate the drying of porous media for complex regular/irregular geometries. (C) 2018 Elsevier Ltd. All rights reserved.