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Developing a Software to Analyze Electroosmotic Flow in Microchannels

Farzinpour, Pouyan | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39573 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. The fabrication of micron-sized instruments MEMS have been in fast progress in different fields of science and technology such as those of chemical processes in chemical engineering, propulsion in aerospace industries, microchip cooling and inkjet printers in electrical industries, and medical appliances in medical and biomedical science. They have forced the manufacturers and researchers to work and think in fabricating such small-scale sizes. However, the complexity of fabricating MEMS with moving parts has also promoted the manufacturers to think of alternative ways. For example the use of moving parts to pump fluid in such devises causes such difficulties and the researchers could adopt alternative techniques like using the electroosmotic phenomenon to pump the fluid. This research presents the numerical simulation of electroosmotic phenomenon, i.e., pumping a polar solvent in a capillary imposing an electric filed along the microchannel. Most of the last electroosmotic phenomenon studies in microchannels have been curried out by either simplifying of Nernst-Planck equations to find the distributions of ions or adopting the Helmholtz-Smoluchowski velocity as the slip velocity imposed at the solid surface. Moreover, those studies have not taken into consideration the effect of reservoirs at the inlet and outlet of the microchannel. This shortcoming can seriously degrade the solution inside the channel. In this research, we present the simulation of electroosmotic phenomenon without the above employed simplifications. The employed governing equations consist of the modified form of the Navier-Stokes equations to solve for fluid flow, the Poisson equation to obtain the electric potential distribution in the EDL, the Laplace equation to calculate the external electric potential distribution, and the Nernst-Planck equations to calculate the positive and negative ion distributions. We use an extended hybrid finite-volume-element method as our numerical tool. The incompressible Newtonian fluid flow equations are solved implicitly. The results show that it is necessary to include two reservoirs at both sides of microchannel to capture the real pressure drop at its both ends correctly. Alternatively, we introduce a novel boundary condition in this work to remove the reservoirs without losing their advantages. Additionally, we study the effect of adverse pressure gradients on electroosmotic flow and show the effect of recirculation and revered flow on mass flow rate inside the capillary
  9. Keywords:
  10. Micronozzle ; Compressible Flow ; Finite Volume Method ; Finite Element Method ; Electroosmotic Flow

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