PROGRAM | Plant and Soil Sciences

By: Wenjuan Zheng Chair: Yan Jin Co-Chair: Lian-Ping Wang

ABSTRACT

Understanding flow in porous media is a challenging problem in many fields of fundamental science and engineering. This dissertation focuses on flow behavior at the pore scale, including observation and simulation of flow in microchannels and development of pore-space-based models for unsaturated hydraulic conductivity. Pore-scale flow is strongly influenced by relatively large interfacial areas (per unit volume) where surface tension, viscosity, and diffusion processes dominate gravity and inertia. Consequently, flow regimes may differ markedly from conventional large-scale flows.
In Chapter 2, I presented water flow patterns visualized in open capillary channels with various sizes using the &mu-PIV technique. I found that a partial-slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the air-water interface (AWI). The mechanism for a partial slip boundary condition at the AWI is due to the confinement of adjoining solid walls. In Chapter 3, I demonstrated that assuming a partial-slip AWI for corner flow could improve the prediction of unsaturated hydraulic conductivity at low water saturation conditions compared to that with a shear-free AWI. A roughness triangular pore space model (R-TPSM) for water retention and unsaturated hydraulic conductivity was developed in Chapter 4. The R-TPSM takes into account surface roughness effects where film flow largely increased at low water content. The model was able to significantly improve the prediction of unsaturated hydraulic conductivity for heavier-textured soils (e.g., loam). In Chapter 5, the slip boundary condition at rough surfaces was resolved numerically at the pore scale. Roughness scale, together with interfacial shape and local slip length at the liquid-gas interfaces, and particularly the coupled effect of the last two, affect the effective slip length on the rough surfaces.
Improved physical understanding of surface/interface effects on multiphase flow behavior at both the pore scale and the core scale has been achieved in this study. Findings in this study are essential for an accurate quantification of a wide variety of multiphase problems in porous media as well as for design and manipulation of flow in microfluidics.

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