Chen, Ching-Hsien (2013) 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. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery
Library of Congress Subject Headings (LCSH):	Microfluidic devices -- Design and construction, Transition flow -- Simulation methods, Microfluidics, Bubbles -- Dynamics, Photography, High-speed
Official Date:	July 2013
Dates:	Date Event July 2013 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Li, Shengcai
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xvii, 199 leaves : illustrations.
Language:	eng

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