Predicting Fluid Configuration and Liquid-Vapor Interfacial Area in Porous Media by Localized Equilibrium Models

The configuration of fluid in unsaturated porous media is important in processes such as environmental remediation, multiphase separations, catalytic reactions, and mass transfer at plant roots. A model developed by Silverstein and Fort predicted the configuration of water in unsaturated porous media by minimizing the interfacial energy utilizing the simulated annealing Monte Carlo based approach to global optimization. This model uses a digitized model space of air, water, and quartz elements, with air and liquid elements rearranged to locate the fluid such that the interfacial energy of the entire system is minimized. The research described here demonstrates the improvements in the ability of the model to represent trends observed in interfacial area measurements which appear to result from quasi-equilibrium configurations at low water contents where liquids have a limited transport ability. The model has been modified to address this limited mobility of liquids at low connectivity by performing localized minimizations of interfacial energy by limiting the distance in which a fluid element can move in a single simulation step. This maximum move distance is a function of particle/pore size and is implemented to account for limited hydraulic conductivity in the system.