The present work contains two parts: nanofluids and bioheat transport, both involving
multiscales and sharing some common features. The former centers on addressing the
three key issues of nanofluids research: (i) what is the macroscale manifestation of
microscale physics, (ii) how to optimize microscale physics for the optimal system
performance, and (iii) how to effectively manipulate at microscale. The latter
develops an analytical theory of bioheat transport that includes: (i) identification and
contrast of the two approaches for developing macroscale bioheat models: the
mixture-theory (scaling-down) and porous-media (scaling-up) approaches, (ii)
rigorous development of first-principle bioheat model with the porous-media
approach, (iii) solution-structure theorems of dual-phase-lagging (DPL) bioheat
equations, (iv) practical case studies of bioheat transport in skin tissues and during
magnetic hyperthermia, and (v) rich effects of interfacial convective heat transfer,
blood velocity, blood perfusion and metabolic reaction on blood and tissue macroscale
temperature fields.
Nanofluids, fluid suspensions of nanostructures, find applications in various
fields due to their unique thermal, electronic, magnetic, wetting and optical properties
that can be obtained via engineering nanostructures. The present numerical simulation
of structure-property correlation for fourteen types of two/three-dimensional
nanofluids signifies the importance of nanostructure’s morphology in determining
nanofluids’ thermal conductivity. The success of developing high-conductive
nanofluids thus depends very much on our understanding and manipulation of the
morphology. Nanofluids with conductivity of upper Hashin-Shtrikman bounds can be
obtained by manipulating structures into an interconnected configuration that
disperses the base fluid and thus significantly enhancing the particle-fluid interfacial
energy transport. The numerical simulation also identifies the particle’s radius of
gyration and non-dimensional particle-fluid interfacial area as two characteristic
parameters for the effect of particles’ geometrical structures on the effective thermal
conductivity. Predictive models are developed as well for the thermal conductivity of
typical nanofluids.
A constructal approach is developed to find the constructal microscopic physics
of nanofluids for the optimal system performance. The approach is applied to design
nanofluids with any branching level of tree-shaped microstructures for cooling a
circular disc with uniform heat generation and central heat sink. The constructal
configuration and system thermal resistance have some elegant universal features for
both cases of specified aspect ratio of the periphery sectors and given the total number
of slabs in the periphery sectors.
The numerical simulation on the bubble formation in T-junction microchannels
shows: (i) the mixing enhancement inside liquid slugs between microfluidic bubbles,
(ii) the preference of T-junctions with small channel width ratio for either producing
smaller microfluidic bubbles at a faster speed or enhancing mixing within the liquid
phase, and (iii) the existence of a critical value of nondimensional gas pressure for
bubble generation. Such a precise understanding of two-phase flow in microchannels
is necessary and useful for delivering the promise of microfluidic technology in
producing high-quality and microstructure-controllable nanofluids.
Both blood and tissue macroscale temperatures satisfy the DPL bioheat equation
with an elegant solution structure. Effectiveness and features of the developed
solution structure theorems are demonstrated via examining bioheat transport in skin
tissues and during magnetic hyperthermia. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174465 |
| Date | January 2012 |
| Creators | Fan, Jing, 范菁 |
| Contributors | Wang, L |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47752853 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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