Wildenschild/Schaap Existing analyses on thin film characteristics in porous domains are often built on two- or quasi-three dimensional geometrically simple pore structures without explicitly accommodating pore connectivity in the third dimension. More in-depth numerical and experimental studies are needed to bridge the gap between two- and three dimensional experimental analyses as well as the gap between three-dimensional numerical and experimental analyses of pore-scale thin-film characteristics in granular porous media. Hence, the proposed research, which builds on our ongoing pore-scale interfacial research, aims at integrating experimental and numerical analyses for better understanding of thin film characteristics and thermodynamics in three-dimensional porous media consisting of interconnected arbitrary rough-walled pore geometries. In this 1-year extension proposal, we aim to develop a thermodynamically sound free-energy-based multiphase lattice-Boltzmann model (that can handle fluids with highdensity contrasts and implements thermodynamically-sound solid-fluid interactions). To obtain data for model verification, we will measure thin film characteristics related to film formation and distribution in a crushed volcanic tuff. This includes imaging water distributions as they progress from adsorbed films to capillary held water with increasing vapor pressure. Based on the images it is possible to estimate the critical separation distance at which capillary condensation takes place. The film characteristics will first be measured in geometrically simple two-dimensional flow channels using time-lapse digital microscopy, and subsequently using computerized microtomography (CMT) for more complex three-dimensional systems in crushed tuff samples. From the CMT images we will determine the location and the extent of the capillary condensed regions to be used to validate new model developments. Once the model is validated using the two-dimensional experimental data, the model will be used to simulate thin film formation and distributions in a threedimensional natural porous medium with hydraulically connected arbitrary pore geometries. Numerically simulated results on the geometry and extent of capillary condensed zones will be compared to the microtomography data. The numerical model will then be used to map the spatial distribution of variables that cannot be measured experimentally such as fluid density, vapor pressure in thin films, interfacial width, and three-dimensional curvatures, to subsequently calculate interfacial energies, surface tension, chemical potentials, and disjoining pressures. Broader Impacts of the proposed research: We expect that the findings from the proposed research could have important wider impacts in diverse fields where processes relevant to the low saturation regime are of significance, including arid zone irrigation and water management, fate and transport of contaminants and colloidal particles in the vadose zone, nuclear waste disposal in very dry climates, enhanced oil recovery, and in planetary sciences. In addition, the project will provide training for undergraduate and graduate students, as well as a post-doc.
