Intelligent Design of Microfluidic Components for Newtonian and Complex Fluid Systems

Download or read book Intelligent Design of Microfluidic Components for Newtonian and Complex Fluid Systems written by Konstantinos Zografos and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Interest in microfluidics has increased dramatically in recent years, with applications spanning a wide range of fields. However, despite several advances, design of microfluidic devices still relies largely on trial-and-error. This thesis aims to go beyond this approach in favour of a rational design of microfluidic devices based on theoretical and numerical design rules and algorithms. More specifically, this research focuses on understanding and controlling fluid dynamics in applications involving complex non-Newtonian fluids in shear and extensional flows. Biomimetic principles and shape optimisation methods are employed to propose new designs for single-phase fluid flow. Furthermore, the single-phase numerical solver is extended to cope with two-phase systems, thus paving the way for new applications of these techniques. Focusing on shear-flows, a biomimetic principle appropriate for fully developed flows has been extended here to be applicable for non-Newtonian fluids, described by the power-law constitutive relationship. The derivation of the principle leads to a biomimetic rule that provides the appropriate dimensions for designing customised microfluidic bifurcating networks, able to generate specific wall shear-stress gradients along consecutive generations. A range of power-law fluids is examined numerically demonstrating great agreement with theoretical predictions. In terms of extensional flow, a range of shapes are proposed for designing microfluidic channels for studies related to the response of complex fluid systems under homogeneous strain-rate. Optimisation techniques are employed for finding the appropriate shapes to generate homogeneous extensional flows along the flow centre line of single stream (contraction-expansion channels) and the multi-stream designs (T-channels and flow focusing devices). The optimised geometries proposed exhibit enhanced performance compared to well defined geometrical shapes. The in-house single phase solver used in all numerical studies is upgraded here in order to solve numerically 3D-problems related to two-phase systems described by the Phase Field method. Here, the code is validated for 2D-problems only, using a range of test-cases demonstrating a very good quantitative agreement. Keywords: Non-Newtonian fluids, Shear-thinning and shear-thickening behaviour, Bifurcating networks, Biomimetics, Optimisation, Extensional flows, Two-phase systems.