UNDERSTANDING MICROFLUIDIC APPROACHES FOR SLURRY DILATION AND SOLID PARTICLE SEPARATION TARGETING WATER FILTRATION

Abstract

In this thesis, a series of experimental and numerical investigations are carried out pertaining to the study of particulate phase migration dynamics in confined channel flows targeting controlled dilation as well as complete separation. A detailed understanding about the physics of inertial migration in microchannel flows is provided, limitations of inertial microfluidic technology at higher particle concentrations are described, and other potential microfluidic ways to achieve controlled dilation and complete separation of medium to high-concentration heterogeneous particle suspensions are investigated. In the first study, A finite element method based numerical framework coupled with Lagrangian point particle approach is used to investigate the migration dynamics of neutrally buoyant particles in straight and spiral microchannel (AR < 1). To separate particles from polydisperse suspensions, a two-stage trifurcation microchannel design is proposed and tested over a wide parameter space. Numerical simulations have depicted different stages of inertial migration for neutrally buoyant particles in straight channels. It has been also shown that the slow migration stage can be effectively bypassed by adjusting the opening width of the separatory branch (bc1). The effect of various factors like branching angle and branching length ratio are investigated and an optimum criterion in terms of momentum distribution value that needs to be maintained at the branching zone is proposed. To extend the applicability of inertial microfluidic technology to heterogeneous particulate suspensions, a hybrid microfluidic design by incorporating alternate contraction-expansion array (ACEA) into spiral design is proposed and tested numerically. This design facilitates complete separation of both buoyant and non-buoyant particles from the suspensions in a continuous manner. In the next work, experimental investigations are carried out for controlled dilation from solid-liquid suspensions at medium to high concentrations slurries. Seven microchannel designs that are commonly reported in the literature are fabricated and their dilation performance is investigated based on residence time of continuous and dispersed phases. An intelligent design that connects several microchannels between inlet and outlet headers with an inlet obstacle pillar array is developed and their effect on dilation performance is tested. From the experimental analysis, the critical parameters that are affecting the dilation performance are found to be channel aspect ratio and flow Reynolds number. An empirical correlation is proposed based on non-linear regression analysis on the experimental data to estimate the dilation performance by varying the above two parameters.