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Electro-Rheological Investigation of Flows and Transport Phenomena in Micro-Nanofluidic Systems

Reshadi, Milad | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55040 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saeedi, Mohammad Hassan
  7. Abstract:
  8. In recent decades, significant advances have been made in the manufacturing of micro/-nanofluidic equipment that can reduce the cost of conducting electrochemical experiments and increase the accuracy, speed, and control of these experiments. In this regard, by installing micro/nano-networks on laboratories on a chip, the above objectives have been made possible. Due to the increase in surface-to-volume with decreasing of size of devices, important surface phenomena such as electrokinetics may reach a special place to control the micro/nanoflow. On the other hand, since each of the materials used in the construction of the above equipment reveals a special property in contact with different electrolytes, flow simulation in micro/nanoconfinements requires the use of comprehensive theoretical models that covers the interval of changes in the zeta potential, rate of fluid-solid interactions and hydrophobic properties of the surface. Also, using the properties of polymer materials in improving surface net electric charge and shear thinning of non-Newtonian fluids in micro/nano scales, two new areas will open up for the study of electro-rheological aspects of flows in pores bonded to the polyelectrolyte brushes and viscoelastic fluids. Due to the lack of analytical and numerical studies in this subject, the purpose of the present thesis is to conduct a detailed study to unravel the electrohydrodynamic aspects of such transfer phenomena by using precise methods including molecular theory approach, generalized dispersion model, Taylor-Aris method and finite difference approximation. To do so, by dividing the problem into three parts including electric potential distribution, velocity and concentration fields, the specifications of the transfer phenomena for two types of flow geometries with circular and rectangular cross sections are investigated. The main results of this study include: increasing / decreasing the degree of ionization of polyacidic/polybasic brushes and, consequently, increasing/decreasing the average velocity level by increasing the pH of electrolyte, drastic increase of the volumetric flow rate of the viscoelastic fluid due to increasing the zeta potential, decreasing the electroosmotic flow rate due to increasing the viscoelectric dimensionless coefficient and decreasing the mixing efficiency by 63% in the range of 0.1 to 10 changes of the zeta potential ratio of the adjacent walls of the micromixer. It is predicted that by the achievements of this dissertation, the transfer processes in lab-on-a-chip devices can be optimized by more precise design of micro/-nanofluidic systems.
  9. Keywords:
  10. Viscoelasticity ; Electrokinetic Process ; Molecular Theory ; Taylor-Aris Model ; Micro/Nano Flows ; Generalized Dispersion

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