| Summary: | 碩士 === 國防大學中正理工學院 === 兵器系統工程研究所 === 92 === The objective of the present study is to develop a numerical model that will enable us to investigate non-Newtonian fluids flow in microchannels with electrokinetic effects. The governing equations are derived from three parts : the first part is solving a nonlinear Poisson equation governing the electric potential which results from potential of solid liquid boundary and the applied electrical potential ; the second part is solving the Nernst-Planck equation governing the ionic concentration distribution ; the third part is solving the Navier-Stokes equations with electrokinetic effects. The third part can be derived from complete Navier-Stokes equations with theories of Power-Law fluids, and extend the applications to the non-Newtonian fluids. So we can solve all the governing equations of the system by the primitive variables. We can change the value of the Power Law index n, and discuss the effects of the shear thinning and shear thickening property on the fluids. When the mathematical model is simplified to Newtonian fluids, the results have good agreement with previous works. That means the programs and numerical methods used in this study are favorable to give reasonable results.
Present results show that, since the stress would change with rate of shearing strain in Power-Law fluids of non-Newtonian, the distribution of velocity in microchannels and the entrance effects are changed with the different Power-Law index n. The synthetic results in this study show that the length of entry region is raised with the Power Law index n , and with the increase of Reynolds number , there will be a concave shape in the velocity distribution in the fully developed region .
Besides, the present study also explores the effects of step change zeta potential to the electroosmotic flow. We find that the electroosmotic flow with step change zeta potential in a microchannel is extremely different from that one with uniform zeta potential. And with the change of the Power Law index n, there will be different characteristic of the electroosmotic flow.
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