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Title: Tools for developing continuous-flow micro-mixer : numerical simulation of transitional flow in micro geometries and a quantitative technique for extracting dynamic information from micro-bubble images
Author: Chen, Ching-Hsien
ISNI:       0000 0004 2749 3845
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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Recent advance in the microfluidics including its fabrication technologies has led to many novel applications in micro-scale flows. Among them is the continuous-flow micromixer that utilizes the advantages associated with turbulent flows for rapid mixing, achieving the detection of fast kinetic reaction as short as tens of microseconds. However, for developing a high performance continuous-flow micromixer there are certain fundamental issues need to be solved. One of them is an universal simulation approach capable of calculating the flow field across entire passage for entire regime from very low Reynolds number laminar flow through transition to fully turbulent flow. Though the direct numerical simulation is potentially possible solution but its extremely high computing time stops itself from practical applications. The second major issue is the inevitable occurrence of cavitation bubbles in this rapid flow apparatus. This phenomenon has opposite effects: (a) deteriorating performance and damaging the micromixer; (b) playing a catalyst role in enhancing mixing. A fully understanding of these micro bubbles will provide a sound theoretical base for guiding the design of micromixer in order to explore the advantage to maximum while minimizing its disadvantages. Therefore, the objectives of this PhD programme is to study the tools that will effectively advance our fundamental understandings on these key issues while in short term fulfil the requires from the joint experimental PhD programme held in the life science faculty for designing a prototype experimental device. During this PhD study, an existing numerical approach suitable for predicting the possibly entire flow regime including the turbulence transition is proposed for simulating the microscale flows in the microchannel and micromixer. The simulation results are validated against the transitional micro-channel experiments and this numerical method is then further applied for the micromixer simulation. This provides the researcher a realistic and feasible CFD tool to establish guidelines for designing high-efficiency and cost-effective micromixers by utilizing various possible measures which may cause very different flows simultaneously in micromixer. In order to study microscale cavitation bubbles and their effects on micromixers, an innovative experimental setup is purposely designed and constructed that can generate laser-induced micro-bubbles at desired position and size for testing. Experiments withvarious micro-scale bubbles have been performed successfully by using an ultra high-speed camera up to 1 million frame rate per second. A novel technique for tracking the contours of micro-scale cavitation bubble dynamically has been developed by using active contour method. By using this technique, for the first time, various geometric and dynamic data of cavitation bubble have been obtained to quantitatively analyze the global behaviours of bubbles thoroughly. This powerful tool will greatly benefit the study of bubble dynamics and similar demands in other fields for fast and accurate image treatments as well.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General) ; TJ Mechanical engineering and machinery