Ionic Size and Rheology Effects on the Mixing Process of Electroosmotic Flows

Ahmadian Yazdi, Alireza | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46930 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saeedi, Mohammad Hassan; Mozaffari, Ali Asghar
  7. Abstract:
  8. In recent years, there have been huge advancements in fabrication of micron-sized devices such that they enabled engineers to create a wide range of miniaturized systems, each of which is utilized in mechanical, electrical, and thermal applications. Micromixers are one of these devices with the role of mixing various micro flows. These devices are broadly used for chemical, biological, and biomedical assays. Among variety of micromixers, one that employs electrokinetic transport phenomenon is of great popularity. For instance, mixing under electroosmotic flow enables accurate process control and eliminates the need for moving components inside micromixer. The very complex nature of electric double layer may impose new and unexplored features under certain circumstances such as high ionic densities or large applied voltage. Such conditions may give rise to important phenomena like ionic size or, as called in pertinent literatures, steric effects which is capable of significant alteration in mixing process. Moreover, most bio-microfluidic devices employ liquids that the rheological behavior of which cannot accurately be predicted by Newtonian law of viscosity. Hence, a deep understanding of rheology and steric effects facilitate the design of future micromixers. In the present study, the analysis is categorized into three major topics. In the first and second one, the influence of ionic finite volumes and non-linear rheology on the micro-mixing process is addressed. Finally, utilizing an analytical approach, the mechanical diffusion, or “Taylor” dispersion, is computed for the micro-scale mass transport under the action of electroosmotic force. On this basis, we proposed an approximate-analytical solution for the mass transport equation which provides accurate prediction of mixing process inside channels with aspect ratios more than 4. Our results have shown that in combined electroosmotic and pressure driven flows, the mixing behavior of various power-law fluids under favorable axial pressure gradient is in sharp contrast with the condition of exerting adverse axial pressure gradient. Moreover, for a wide range of flow behavior index, the steric effects accelerate the mixing process by retarding the flow, while for liquids with large flow behavior index these effects may delay the completion of mixing
  9. Keywords:
  10. Electroosmotic Flow ; Power-Low Fluid ; Microfluidic Devices ; Micromixer ; Rheological Properties ; Ionic Size Effect ; Taylor Diffusion

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