Biggs, Mark JamesAlwahabi, Zeyad T.Zhang, HuElekaei Behjati, Hamideh2016-11-302016-11-302016http://hdl.handle.net/2440/102887Microfluidic devices are utilized in a wide range of applications, including micro-electromechanical devices, drug delivery, biological diagnostics and micro-fuel cell systems. Of particular interest here are liquid-liquid microfluidic systems; which are used in drug discovery, food and oil industry amongst others. Increased understanding of the fundamentals of flows in such devices and an improved capacity to design them can come from modelling. In the case of liquid-liquid flows in microfluidic systems, it is necessary to explicitly model the behaviour of the individual liquid phases. Such explicit numerical simulation (ENS) as it is termed requires advanced numerical methods that are able to evaluate flow involving multiple deforming fluid domains within often complex boundaries. Smoothed Particle Hydrodynamics (SPH), a Lagrangian meshless method, is particularly suitable for such problems. This use of a CFD allows determination of parameters that are difficult to determine experimentally because of the challenges faced in microfabrication. The study reported in this thesis addresses these concerns through development of a new SPH-based model to correctly capture the immiscible liquid-liquid interfaces in general and for a microfluidic hydrodynamic focusing system in particular. The model includes surface tension to enforce immiscibility between different liquids based on a new immiscibility model, enforces strict incompressibility, and allows for arbitrary fluid constitutive models. This work presents a detailed study on the effects of various flow parameters including flowrate ratio, viscosity ratio and capillary number of each liquid phase, and geometry characteristics such as channel size, width ratio, and the angle between the inlet main and side channels on the flow dynamics and topological changes of the multiphase microfluidic system. According to our findings, both flowrate quantity and flowrate ratio affect the droplet length in the dripping regime and a large viscosity ratio imposes an increase in the flowrate of the continuous phase with the same capillary number of the dispersed phase to attain dripping regime in the outlet channel. Also, increasing the side channel width causes longer droplets, and the right-angled design makes the most efficient focusing behaviour. This study will provide great insights in designing microfluidic devices involving immiscible liquid-liquid flows.smoothed particle hydrodynamicsimmiscible liquid-liquid microfluidicssurface tensionincompressibilityhydrodynamic focusingTheses10.4225/55/583e616dc4a85