Optimisation of Microfluidic Flow Systems

This project investigates the fluid flow and heat transfer in microfluidic flow systems using Computational Fluid Dynamics (CFD) and experiments. The first part of this work focuses on developing a CFD - enabled optimisation methodology of the geometrical features of i) a microfluidic heatsink design and ii) a single-phase (SP) continuous-flow (CF) Polymerase Chain Reaction (PCR) Device. This is achieved using COMSOL Multiphysics 5.4 ®to simulate the fluid flow, heat transfer (and PCR kinetics for the case of the microfluidic PCR device). Optimisation problems are then formed, selecting objective functions related to the performance of the devices. Design of Experiments is then used together with COMSOL Multiphysics 5.4 ® to collect the values of the objective functions over the design domain. Matlab© is then used to generate the response surfaces of the objective functions, using different techniques, locate the optimum design solutions (genetic algorithm, multi-level coordinate search method) and obtain the Pareto front for the cases of multi-objective optimisation problems. Results of this work indicate the possibility of significantly enhancing the performance of SP-CF-PCR devices in terms of the DNA amplification, device volume, total operating time and total pressure drop by up to 16.4%, 43.2%, 17.8% and 80.5% respectively, after applying the appropriate design modifications for each objective. The increase in the DNA amplification is achieved by increasing the channel width and residence times while minimising the channel height. The reduction in the device volume, total operating time and total pressure drop are achieved when using the smallest residence times and higher channel width. According to this investigation, the DNA amplification appears to be linked to the temperature uniformity and to the residence time in the extension zone. The second part of this work focuses on i) obtaining a better understanding of the role that the concentration and presence of droplets play in conjugate heat transfer phenomena in droplet-laden flows, ii) creating and optimising a reusable, cheap and easy-to-fabricate device that can perform Melting Curve Analysis (MCA), in order to facilitate the work of a group of biologists at the University of Leeds. More specifically, this device aims to check for the presence of rare DNA species and possible contaminations in their collected samples in a fast, robust and cheap way, by testing if the DNA product has a unique melting temperature. The experimental setup is designed after performing a series of simulations using COMSOL Multiphysics 5.4 ®, considering different potential designs while at the same time simulating the energy requirements of the system. After finalising the design, a PID temperature controller is implemented on the Arduino Platform, achieving the required temperature difference between the two ends of the device. The results obtained during the experiments demonstrate a successful temperature control that is robust and does not require the adjustment of the PID parameters for the performance of similar experiments in the different temperature ranges tested.