Theoretical Study on Coupling Mechanisms of Microflow and the application in Microfluidics Systems
| Autor: | Li Wen-Ken, 李汶墾 |
|---|---|
| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 The present study is concerned with a theoretical analysis for photophoresis of a micro particle subjected to a uniform intense light in a gaseous or aqueous medium. The direction of the photophoretic force can be determined by the sign of the asymmetry factor. Depending on optical property of the particle, it is found that the variation of photophoresis with particle size has three patterns, viz., (a) negative photophoresis prevailing pattern; (b) normal switching of photophoresis; and (c) positive photophoresis dominant pattern. Based on the Mie theory, the asymmetry factor, heat source function, and photophoretic force and velociry at various conditions are evaluated, and the influences of particle size, refractive index and absorptivity are explored systematically. Different from previous studies with simple velocity slip condition, thermal stress slip flow due to variation of normal heat flux along the gas-solid interface is taken into account. The analytic expressions and the order-of-magnitude analysis demonstrate that the present theory agrees well with the measured data especially at smaller particle sizes. As to the photophoresis in liquids, a novel theory is developed by combining the conventional photothermal analysis for general particle phoretic motion and the concept of solvent molecular interactions employed for force evaluation of thermophoresis in liquids. An analysis for photophoretic velocity is performed systematically on the influences of particle characteristics such as size, optical properties, hydrophobicity, and thermal conductivity. Heat source function and the corresponding asymmetry factor at various conditions are evaluated to interpret the mechanisms of negative and positive photophoresis and the conditions for transition between them. In the present study, photophoresis in gases and liquids are investigated in detail for further understanding of the coupling mechanisms with complex multi-physics interactions. This study is expected to be useful in analysis and design of opticfluidics devices for particles manipulation and other related applications. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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