Numerical Simulation Of Power-law Fluids Electroosmosis Modulation And Thermal Effects In Microchannels

Various physical, chemical and other operations can be realized through the control of fluid in microscale space on the microfluidic chips, which are widely used because of its small size, low cost, fast response and high precision characteristics. As the most important delivery technique for microfluids, electroosmosis is widely used in microfluidic system of liquid transportation, mixing, reaction and separation. This paper had carried on the theoretical analysis and numerical simulation of electroosmosis modulation and non-isothermal electroosmotic flow(EOF) in microchannels, which had a guiding significance on the development and application of microfluidic chips. The main research work and achievements are as follows:Based on PB model and PNP model, this paper had studied the characteristics of EOF in a parallel flat microchannel through numerical simulation and experimental validation, revealed the micro/nanoscopic liquid flow nature of Newtonian fluids and non-Newtonian power-law fluids. Analysis showed that the EOF of power-law fluid nonlinear reduces with the increase of power-law index and electrokinetic parameter, and the flow pattern also changes. The variation of applied electric field and zeta potential makes the EOF of power-law fluid nonlinear changes, but the flow pattern remains the same.A numerical simulation was investigated on the flow and heat transfer of the EOF in microchannel under two kinds of typical thermal boundary conditions based on the PNP model with universality. Multiphysics coupling of the electric field, flow field, concentration field and temperature field was implemented and the temperature-dependent properties of fluid were also considered. The results show that a proper control of thermal field can lead to various non-plug-like flow patterns. A constant vertical temperature difference across the channel causes a shear flow, the horizontally-varying thermal condition generates fluctuating flow, the alternating vertical temperature gradient induces a wavy flow. The ion distribution in microchannle changes with the difference of temperature gradient, the phenomenon is that ion concentration in low wall temperature region is higher than high wall temperature region, and the periodic motion of ions lags behind the change of temperature field.A numerical simulation of a flow in a parallel flat microchannel with heterogeneous zeta potential along the channel walls was carried out, and the effects of non-Newtonian power-law fluids on micromixing had been studied. The results show that a difference in shear-dependent viscosity affects electrokinetic phenomena and the mixing efficiency. Shear-thinning/shear-thickening characteristics of fluids tend to enhance/weaken electrokinetic phenomena. With a decrease in the fluid behavior index, a more homogeneous solution is obtained. Electroosmotic micromixing is found to be more practical and efficient in pseudoplastic fluids rather than those Newtonian and dilatant ones. The mixing performance can be improved by adjusting the applied electric field and zeta potential. Pseudoplastic fluids are more sensitive than Newtonian and dilatant fluids to the parameters.