【作者】 赵亮；

【导师】 刘林华；

【作者基本信息】 哈尔滨工业大学 ， 工程热物理， 2009， 博士

【摘要】 随着微流体机械和微全分析系统的迅速发展,微通道得到了广泛的应用。例如微电子器件的冷却、基于微流动的MEMS设备、微执行器、微型泵、微型混合器、微型阀和芯片实验室等。微通道内的流体流动和热传递已经成为一个重要的研究领域,对微通道内的流体流动和热传递性质的研究,对这些微小型设备的优化设计十分重要。电动效应使得微通道内的流动和热传递受通道尺寸和流体性质的影响存在反常特性,产生电动效应的主要原因是微通道壁面存在双电层。因为水分子为极性分子,凡是和水溶解接触的表面一般都会产生静电荷,在微通道表面的电荷会使溶液中的阴、阳离子重新分布,导致了双电层的形成。当电动效应对流动所产生的作用力与传统的驱动力在一个数量级上,那么电动效应就不能被忽略。本文通过数值求解描述壁面电势分布的Possion方程,控制离子分布的Nernst-Planck方程和增加了电动效应源项的动量方程与能量方程,研究了在电动效应作用下,微通道内液体的流动特性、热传递特性以及电动效应在微混合、粒子分离和微执行器等方面的应用。主要工作包括以下五个方面:1.研究了微通道壁面双电层交叠时,电动效应对微通道内压力驱动流发展段的影响,分析了壁面双电层对微通道内流体的速度场,温度场,压力梯度及水力摩擦因子的影响,指出流动电势是影响电动效应作用下微通道内压力驱动流流动特性的主要因素。2.分别采用Boltzmann方程和Nernst-Planck方程描述离子分布,研究了平行平板微通道电渗流入口段的流动特性,分析了雷诺数、κh值和外加电场对微通道电渗流的影响。研究了辐射对电渗流流动的影响,给出在不同辐射热流密度和介质吸收系数情况下,微通道内流体的温升。系统地分析了开口和闭口微通道电渗流的熵产,讨论了导热熵产、粘性耗散熵产和焦耳热熵产之间的关系。从强化换热和提高系统能量转换效率的角度来说,应该选择较小的外加电场强度。3.提出了采用施加横向电场和利用闭口微通道电渗流的环流特性来提高微通道内混合效率的方法。研究了外加电场强度、微通道高度和电极对密度对微混合的影响,指出微通道高度越小,电极对密度越大越有利于混合。分析了焦耳热和微通道内温度梯度对微混合的影响。4.采用拉格朗日轨迹追踪法,数值模拟了在不同电场作用下,具有不同电泳淌度的粒子在微通道内的运动情况,给出粒子分离效率随外加横向电场强度和粒子电泳淌度的变化规律。5.基于利用闭口微通道结构作为微执行器使用的应用背景,分析了在不同微通道高度,不同外加电场强度,不同壁面zeta电势和不同对流换热系数情况下,焦耳热对闭口微通道电渗流流动特性的影响。研究了等温边界条件和对流边界条件情况下,焦耳热对闭口微通道电渗流流动特性的影响。指出在等温边界条件下,考虑焦耳热时的诱导压力梯度比不考虑焦耳热时的诱导压力梯度小。更多还原

【Abstract】 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.更多还原