Date of Award

8-2016

Degree Name

Master of Science

Department

Chemical and Paper Engineering

First Advisor

Dr. Dewei Qi

Second Advisor

Dr. Said Abubakr

Third Advisor

Dr. James Springstead

Access Setting

Masters Thesis-Campus Only

Restricted to Campus until

8-2017

Abstract

The behavior of solid particles in a fluid has become an important topic. The need to improve our understanding of the mechanisms of fluid-particle interaction is the motivation for the present work. The characteristics of fibers suspensions depend on the many variables such as flexibility, Reynolds numbers, density and aspect ratio. The aim of this work is to probe effects of these variables on sedimentation behavior by using a fiber-level simulation technique. In this techniques, a D3Q15 model in a lattice Boltzmann equation with a Bhatnagar-Gross-Krook (BGK) approximation is used to simulate motion of fluids, where Navier-Stokes equations are solved equivalently. Meanwhile, a lattice spring model is utilized to mimic the deformation of flexible fibers. The interaction between fluid and solid fiber is handled by an immersed boundary method. Dynamic motion of a single flexible fiber and two flexible fibers settling in an infinite long fluid column at low and moderate Reynolds numbers are numerically simulated in a three dimensional space. The fiber flexibility and density are varied at different levels and their effects on sedimentation are studied. In the simulations, cuboid and cylindrical fibers at different aspect ratios are considered. It is demonstrated that the fiber flexibility has an important impact on fiber position, settling velocities, and fluid structures, where the drafting, kissing, and tumbling (DKT) mechanisms play important roles. The simulation results provide useful information, at a microscopic level, which may not be easily measured in a lab environment.

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