Interfacial Instabilities of Suspensions in Hele-Shaw Cell
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The objective of this research is to investigate the interfacial instability of suspensions in a Hele-Shaw cell, which involves a dynamical coupling between particle transport and fluid-fluid interfacial deformations. Interfacial instabilities have remained an important subject of research given their complicated nature. They are commonplace in multiphase flows such as enhanced oil recovery, lung airways and micro-fluidic droplets, and controlling them is of critical importance. The inclusion of particles in fluid flows can also modify the interfacial dynamics, which yet remains not well understood. The Saffman-Taylor fingering instability occurs when a less viscous fluid displaces a more viscous one in porous media, which has been extensively studied for decades. The interface is supposed to be stable in the reverse scenario, in which the more viscous fluid invades the less viscous one. Surprisingly, the inclusion of particles can fundamentally change the interfacial dynamics and even lead to interfacial instability in the absence of the unstable fluid viscosity ratio. This instability phenomenon was first reported by Tang et al and extended to squeezing suspension flows by Ramachandran. However, the research on this topic has remained qualitative. In this research, we carry out rigorous experiments to characterize the fingering instability introduced particles, by varying the particle volume fraction and the gap thickness over particle diameter ratio h=D. The experimental data are analyzed utilizing advanced image processing techniques to aid our understanding of the phenomenon. Theoretically, we use the suspension balance model to validate the shear-induced migration upstream of the expanding interface and successfully explain the mechanism behind fingering. The project is then extended to bi-disperse suspensions. The experiments are conducted with particles having different diameters by varying both the bulk particle concentration and the respective concentration of each particle species. We observe similar fingering patterns and find that the addition of small amount of large particles leads to an earlier onset of fingering. The suspension balance model is modified to accommodate the bi-disperse suspension system and then utilized to quantitatively explore the dynamics.
Xu, Feng (2017). Interfacial Instabilities of Suspensions in Hele-Shaw Cell. Doctoral dissertation, Texas A & M University. Available electronically from