SUMMARY

Particle suspensions are important both in nature and in industry. The complex nature of hydrodynamic interactions between the particles and the solvent makes such analysis difficult that often requires numerical modeling to understand the behavior of particle suspensions. In this dissertation, we introduce a hybrid computational model that integrates lattice spring model for solid dynamics and lattice Boltzmann method for fluid solver. We use this model to study several practical problems involving the dynamics of spherical, spheroidal particles and deformable capsules in dilute suspensions. The results of our studies disclose the importance of particle dynamics in pressure-driven channel flow and the nonlinear effect associated with fluid inertia leading to particle cross-stream migration. This information not only give us a fundamental insight into the dynamics of particles under dilute suspensions, but also yield engineering guidelines for designing high throughput microfluidic devices for sorting and separation of synthetic particles and biological cells. We first demonstrate that spherical particles can be size-separated in ridged microchannels. Specifically, particles with different sizes follow distinct trajectories as a result of the nonlinear inertial effects and secondary flows created by diagonal ridges in the channel. Then, separation of biological cells by their differential stiffness is studied and compared with experimental results. Cells with different stiffness squeezed through narrow gaps between solid diagonal ridges and channel wall and migrate across the microchannel with different rate depending on their stiffness. This deformability-based microfluidic platform may be valuable for separating diseased cells from healthy cells, as a variety of cell pathologies manifest through the change in mechanical cell stiffness. Finally, the dynamics of spheroid particles in simple shear and Poiseuille flows are studied. Stable rotational motion, cross-stream migration, and equilibrium trajectories of non-spherical particles in flow are investigated. Effects of particle and fluid inertia on dynamics of particles are disclosed. The dependence of equilibrium trajectory on particle shape reveals a potential application for shape based particle separation.