An experimental study of drying in porous media in novel 2D micromodels with dual porosity

Abstract

Drying of porous media is pervasive in numerous natural and engineering processes, such as oil recovery, CO 2 storage, and critical zone science. Drying is essentially a multiphase flow process, where the liquid phase evaporates and is displaced/replaced by the gaseous phases, as vapor diffuses out of the porous structure. In terms of pore structure and other physical characteristics like porosity and permeability, many porous matrices exhibit multi-scale heterogeneity. For instance, in critical zone, soil is often viewed as a hierarchical organization: primary particles form aggregates, which in turn form macroaggregates, effectively leading to a dual-porosity medium. Numerous activities, including gases and water transport, are known to be controlled by the resultant multiscale flow dynamics and inter-/intra-aggregate interaction during drying. However, the fundamental physics underlying drying of porous media with dual porosity is not well understood from a fluid mechanics perspective. In this work, a novel 2D microfluidic device fabrication technique has been developed. To study the multi-phase flow of air and water, emphasizing the multi-scale interaction, pore structure, and role of film flows, three distinct types of microfluidic devices have been fabricated, which bear the innovative three-layer glass-silicon- glass architecture, providing precise structural control and excellent optical access from both top and bottom. An innovative dual-magnification imaging technique has been introduced adapted for micro-PIV and epi-fluorescent microscopy which offers insightful information about the flow dynamics at both the micro- and macro-scales concurrently. In this thesis, two distinct types of experiments are outlined, focusing on diffusion-driven drying and flow-through drying, utilizing three diverse micromodels characterized by varying porous structures and distributions. The experimental results have presented the overall drying dynamics observed in different micromodels, each featuring unique porous configurations. The impact of porous geometry and external flow conditions on drying rate and associated pore-scale physics is thoroughly examined. The findings encompass a comprehensive overview of micro-macro pore interactions, as evidenced by separated saturation distribution, displacement rates, and other pertinent flow parameters. The findings have reflected the influence of pore geometry, distribution, hydraulic connectivity, and film flow on the observed effects.