Liquid Flow Characteristics In Micro-Channel With Electrokinetic Effects

With the rapid development of micro-fluidic device and .micro total analysis system, the micro-channels have been widely used, such as the cooling of micro-electronic device, MEMS device based on micro-flow, micro-actuator, micro-pump, micro-mixer, micro-valve and lab-on-a-chip. The liquid flow and heat transfer in the micro-channel have become an important research area. The research of liquid flow and heat transfer in the micro-channel is very important to the optimization design of these micro-devices.The electro-kinetic effect causes the liquid flow and heat transfer in the micro-channel behaving some unusual characteristic under the influence of channel size and liquid property. It is well known that most surfaces acquire a certain amount of electrostatic charges when brought in contact with aqueous solutions due to the asymmetric dipoles of water molecules. The presence of such charges on the micro-channel surface causes both counter-ions and co-ions in the liquid to be preferentially redistributed which leads to the formation of the electrical double layer. When the applied force due to electro-kinetic effect is compared with the conventional driven force, the electro-kinetic effect can not be neglected.This paper simulates the Poisson equation which is used to describe the surface potential distribution, the Nernst-Planck equation governing anion and cation distributions and the modified momentum equation and energy equation with the additional electro-kinetic effect source term. The paper investigates the characteristic of liquid flow and heat transfer in the micro-channel with the electro-kinetic effect and its application in micro-mixing, particle separation and micro-actuator. The scope of present research contains five parts:1. The electro-kinetic effect on the developing flow driven by pressure in the micro-channel is investigated with the surface electrical double layer overlapping. The liquid velocity field, temperature field, pressure gradient and hydraulic friction factor are studied. The results show that the streaming potential has a great influence on the pressure driven flow with electro-kinetic effect in the micro-channel.2. The electro-osmotic flow in the parallel flat at the inlet is researched by using Boltzmann equation and Nernst-Planck equation to describe the ion distribution respectively. The effects of Reynold number,κh value and applied electric field on the electro-osmotic flow in the micro-channel are investigated. The influence of radiation on the electro-osmotic flow is studied. The liquid temperature increment in the micro-channel is presented under different radiative heat fluxs and medium absorption coefficients. The entropy generations of open-end and closed-end electro-osmotic flow are systematically researched. The relations among the entropy generation of heat conduction, viscous fluid friction and Joule heating are discussed. We should choose the smaller applied electric field to the purpose of strengthening heat transfer and increasing the energy conversion efficiency of the system.3. The methods of applying transverse electric field and utilizing the circulating flow characteristic of the closed-end electro-osmotic flow are presented to improve the mixing efficiency. The effects of applying electric field intensity, micro-channel height and electrode couple density on the micro-mixing are researched. The results show that the smaller micro-channel height and larger electrode couple density are beneficial to micro-mixing. The influences of Joule heating and temperature gradient on the micro- mixing are studied.4. The movement of particle in the micro-channel is investigated with different applied electric fields and particle electro-phoresis mobilities by using Lagrangian tracking method. The effects of transverse applied electric field and particle electrophoresis mobility on the separation efficiency are presented.5. Basing on the application of closed-end micro-channel structure as micro-actuator, the Joule heating effect on a closed-end electro-osmotic flow in the micro-channel is researched under different micro-channel heights, applied electric fields, surface zeta potentials and heat convection coefficients. The influence of Joule heating on the induced pressure is investigated under isothermal boundary condition and convection boundary condition. The induced pressure gradient with considering Joule heating is smaller than that without considering Joule heating with isothermal boundary condition.