Numerical simulation of restructuring behavior of non-fractal aggregate in simple shear flow

by Tu Uyen Lieu

Institution: Hokkaido University
Year: 2016
Posted: 02/05/2017
Record ID: 2101361
Full text PDF: http://hdl.handle.net/2115/61795


Understanding the behavior of colloidal aggregates in fluid flow is one of the fundamental issues for the prediction and control of the dispersion state of colloidal suspension, which is widely encountered in several engineering fields. The structure of the aggregate has a significant role for both the microstructure and macroproperties of the dispersion. An aggregate may vary its structure by three aspects: aggregation with the other to form a larger one, breakup into several smaller pieces, and restructuring i.e. the particles composing aggregate changes their position relatively but still connect to the others. It has been found out that the restructuring not only changes structure of the aggregate itself, but also has a crucial impact on the aggregation and breakup. Therefore, the restructuring of aggregate contributes important role on the overall performance of the dispersion. Recent studies have suggested that in simple shear flow, a widely used model flow system, the aggregate is apt to have high fractal dimension, and the behavior of such aggregates is complicatedly diverse. Consequently, the restructuring behavior of aggregate having high fractal dimension in simple shear flow is important for either understanding the mechanism of restructuring, or developing highly accurate model predicting the properties of dispersion. In this study, the restructuring behavior of non-fractal aggregate in simple shear flow is investigated. Numerical simulation is conducted to examine the effect of aggregate structure and shear flow condition on the restructuring of aggregate, and the underlying mechanism. The aggregate is composed of a number of monosized, spherical, and hard primary particles. The attraction between particles is calculated by the retarded van der Waals potential. For a system of many particles in fluid medium, the hydrodynamic interaction is very important for a dynamical system, yet very complicated. Stokesian dynamics is a simulation technique which is capable of capturing the complex many-body hydrodynamic interaction. Therefore, Stokesian dynamics approach is employed in the study. The dissertation consists of six chapters. Chapter 1 presents the background and the statement of the study. The gap between the recent studies and this work is also given. Chapter 2 gives details of the numerical simulation, including the construction of the mathematical ormulation, the way it is applied to the study, verification of the method, and the simulation conditions of the study. In Chapter 3, the restructuring behavior of a non-fractal aggregate in simple shear flow is explored. The effect of initial coordination number and the intensity of shear flow on the restructuring of aggregate is investigated. The temporal change in internal structure of the non-fractal aggregate, in terms of coordination number, is examined. It shows that after subjected to shear flow, the aggregate…