微通道周期流动电位势及电粘性效应

求解了双电层的Poisson-Boltzmann方程和流体运动的Navier-Stokes方程,得到在周期压差作用下,二维微通道的周期流动电位势,流动诱导电场和液体流动速度的解析解．量纲分析表明,流体电粘性力与以下3个参数有关:1) 电粘性数,它表示定常流动时,通道最大电粘性力与压力梯度的比;2) 形状函数,它表示电粘性力在通道横截面的分布形态; 3) 耦合系数,它表示电粘性力的振幅衰减特征和相位差．分析结果表明,微通道周期流动诱导电场、流动速度与频率Reynolds数有关．在频率Reynolds数小于1时,流动诱导电场随频率Reynolds数变化很慢．在频率Reynolds数大于1时,流动诱导电场随频率Reynolds数的增加快速衰减．在通道宽度与双电层厚度比值较小情况下,电粘性效应对周期流动速度和流动诱导电场有重要影响．     

异质材料有限长微通道电渗流热效应

采用数值方法,分析有限长PDMS/玻璃微通道电渗流热效应．数值求解双电层的Poisson-Boltzmann方程,液体流动的Navier-Stokes方程和流-固耦合的热输运方程,分析二维微通道电渗流的温度特性．考虑温度变化对流体特性（介电系数、粘度、热和电传导率）的反馈效应．数值结果表明,在通道进口附近有一段热发展长度,这里的流动速度、温度、压强和电场快速变化,然后趋向到一个稳定状态．在高电场和厚芯片的情况下,热发展长度可以占据相当一部分的微通道．电渗流稳定态温度随外加电场和芯片厚度的增加而升高．由于壁面材料的热特性差异,在稳定态时的PDMS壁面温度比玻璃壁面温度高．研究还发现在微通道的纵向和横向截面有温度变化．壁面温升降低双电层电荷密度．微通道纵向温度变化诱发流体压强梯度和改变微通道电场特性．微通道进流温度不改变热稳定态的温度和热发展长度．     

电渗流中传热传质过程与熵的分析

在壁面存在恒定热通量条件下,分析微通道内电渗流中传热传质过程与熵的生成.建立数值计算模型,分别采用Poisson-Boltzmann方程、Navier-Stokes方程、Nernst-Planck方程和能量方程来描述微通道内双电层电势、流场、离子浓度和温度的分布情况.引入熵产生,进一步研究不同流动参数对流体传热过程的作用,讨论不同流动参数下各热效应的变化规律,并具体分析热效应参数对流体总熵增加及各部分热效应对总熵比重的影响.结果表明,动电参数与Joule(焦耳)热系数的增大会使得传热性能减弱,动电参数对传热性能影响更为明显;流体的总熵为动电参数、传质系数和质量弥散系数的增函数.     

储层岩石周期性电渗流特性的微观机制

以双电层电位理论和电渗流动的动量方程为基础,结合储层岩石平行毛管束模型,推导出岩石孔隙内周期性电渗流的解析式,揭示了储层中电渗效应的微观机制,分析了非密闭储层岩石中宏观电渗Darcy速度及密闭储层中电渗压力系数频散特性的影响因素．数学模拟结果表明:储层岩石孔隙中,周期性电渗流速度剖面在频率较高时呈“波浪”状;孔隙度越大,电渗Darcy速度模值越大,其相位也越大,而电渗压力系数数值越小．储层岩石的溶液浓度越小或阳离子交换量越大,电渗Darcy速度模值和电渗压力系数数值越大,但对电渗Darcy速度的相位没有影响．     

生物芯片无阀压电微流体泵流场数值研究

采用浅水波模型把浅薄形微泵的三维流动近似为二维厚度平均流动, 并采用有限元/压强修正法求解水平流场和计算微泵流量A·D2数值结果表明:1) 在微泵扩散管的过流截面上流速有时间相位差和回流现象．2) 微泵在吸流末期泵腔出现对称旋涡．3) 微流体泵的定向净流量来自于Navier-Stokes方程的非线性．还给出微泵流量与扩散管长宽比、厚宽比、液体粘度和进出口反压差的定量关系．通过参数优化可以使微泵得到尽可能大的流量．     

柔性圆柱形微管道内的电动流动及传热研究

研究了在纯压力驱动下,流体通过壁面带有某种电荷的聚电解质层（PEL）的微管道，即柔性微管道的电动流动和热传输特性.基于先前得到的电势和速度的解析解以及流向势的数值解,在热充分发展的情况下, 假设壁面热流恒定,利用有限差分法求解了包括黏性耗散和Joule(焦耳)热影响下的能量方程，获得了无量纲温度数值解.通过数值计算，给出了相关的无量纲参数对速度、温度以及Nusselt(努赛尔)数的影响.研究表明,当其他参数固定时,无量纲速度和温度随着无量纲聚电解质层厚度d的增大而减小,随着聚电解质层中等效双电层厚度与双电层厚度之比K_λ的增大而增大；Nusselt数随着Joule热系数S的增大而减小,随无量纲聚电解质层厚度d的增大而减小,随着K_λ的增大而增大.     

微通道内电渗压力混合驱动幂律流体流动模拟

为了研究微通道内电渗压力混合驱动幂律流体的流动特性,建立了微通道内电渗压力混合驱动幂律流体的计算模型,其双电层电势、流体的流场分布分别由Poisson-Boltzmann(P-B)方程和Navier-Stokes(N-S)方程描述.讨论了无量纲Debye(德拜)参数K、壁面ζ*电势和幂律指数n对流体流动特性和Poiseuille数的影响.结果表明,当压力梯度与外加电场方向一致(Γ0)时,剪切变稀流体的速度大于剪切变稠流体;压力梯度与外加电场方向相反(Γ0)时,结果相反.Poiseuille数是无量纲Debye常数K、壁面ζ*电势和幂律指数n的增函数.     

矩形微通道热沉内单相稳态层流流体的流动与传热分析

采用解析方法分析了矩形微通道热沉内单相稳态层流流体的流动与传热．基于y方向流速和导热不变的假设,建立流体在矩形微通道内流动的流速方程和传热的温度方程,进而推导出Nusselt数和Poiseuille数的理论表达式．通过计算结果可以看出,推导的Nusselt数和Poiseuille数的解析解与其他文献的结果吻合较好,而且当宽高比趋于无穷大时,Nusselt数和Poiseuille数分别趋近于8.235和96,这与其他文献结果完全相同．在Reynolds数相同时,摩擦因数随着宽高比的增加而增加,而在相同宽高比时,摩擦因数随Reynolds数的增加而减小．     

等边三角形微通道内层流的流动特性和换热特性的研究

研究等边三角形截面微通道内充分发展层流的流动特性和换热特性,基于Navier-Stokes方程的基本理论,在等边三角形一边向流体加入定常热流密度时,给出了微通道内充分发展层流的速度分布和温度分布的近似解,以及微通道内充分发展对流传热的摩擦因子和Nusselt数;并通过商业软件Fluent对微通道内的流动和换热进行数值模拟,得到通道内温度和速度的数值解,进而计算得到充分发展对流传热的摩擦因子和Nusselt数;二者进行对比,结果吻合很好,验证了计算结果的正确性.     

锥形微通道内液滴自输运特性及力学驱动机制研究

针对液体在微通道内的自输运特性,采用数值仿真与能量解析相结合的方法研究了液滴在锥形微通道内的自输运特性及力学驱动机制,得到微通道的锥形角、液滴与微通道内壁的接触角及微通道的润湿性对液滴自输运特性的影响关系.分析表明,微通道的锥形角、液滴与微通道内壁的接触角均能影响液滴的自输运方向及驱动力大小.对于亲水性微通道,微通道的锥形角、液滴与微通道内壁的接触角其作用效果呈现整体形态;对于疏水性微通道,微通道的锥形角、液滴与微通道内壁的接触角其作用效果呈现局域形态.这可为研究液体在微通道内的自输运机理及界面内液体细观流动机制奠定理论基础.     

Coupled lattice Boltzmann method for simulating electrokinetic flows: A localized scheme for the Nernst–Plank model

We present a coupled lattice Boltzmann method (LBM) to solve a set of model equations for electrokinetic flows in micro-/nano-channels. The model consists of the Poisson equation for the electrical potential, the Nernst–Planck equation for the ion concentration, and the Navier–Stokes equation for the flows of the electrolyte solution. In the proposed LBM, the electrochemical migration and the convection of the electrolyte solution contributing to the ion flux are incorporated into the collision operator, which maintains the locality of the algorithm inherent to the original LBM. Furthermore, the Neumann-type boundary condition at the solid/liquid interface is then correctly imposed. In order to validate the present LBM, we consider an electro-osmotic flow in a slit between two charged infinite parallel plates, and the results of LBM computation are compared to the analytical solutions. Good agreement is obtained in the parameter range considered herein, including the case in which the nonlinearity of the Poisson equation due to the large potential variation manifests itself. We also apply the method to a two-dimensional problem of a finite-length microchannel with an entry and an exit. The steady state, as well as the transient behavior, of the electro-osmotic flow induced in the microchannel is investigated. It is shown that, although no external pressure difference is imposed, the presence of the entry and exit results in the occurrence of the local pressure gradient that causes a flow resistance reducing the magnitude of the electro-osmotic flow.     

Mush–Chimney Convection

Mush–chimney convection occurs in a system consisting of a layer of mixed solid and liquid bounded by liquid above and solid below. The solid phase of the mush is composed of the denser constituent of the alloy, making the residual liquid compositionally buoyant as solidification proceeds. The liquid is in steady, nonlinear convection, consisting of a downward flow in the mush and an upward flow in a chimney, free of solid, which formed spontaneously in the mush as a result of the interaction between flow and structure. A well-posed continuum mathematical model of this system is developed. A novel feature of this analysis is the development of an equation that determines the chimney radius. Material diffusion is an essential ingredient in this equation, but is negligible elsewhere. In the parameter range considered, the problem is well posed without the necessity of specifying the condition of marginal phase equilibrium. A remarkably simple analytic solution is obtained for the convective flow in the chimney.     

Effect of temperature-dependent properties on electroosmotic mobility at arbitrary zeta potentials

A theoretical analysis to determine the electroosmotic mobility in an electroosmotic flow (EOF) in a microchannel at arbitrary zeta potentials is conducted in this study. As an important characteristic in this work, we consider that the wall zeta potentials of the microchannel and the viscosity and electrical conductivity of the electrolyte solution vary with temperature. The flow and the electric and temperature fields are obtained using lubrication approximation theory (LAT) together with the application of the regular perturbation technique. The electroosmotic mobility is evaluated, showing an increase higher than 18% (for the values of the physical properties used in this work) when physical properties, including the zeta potential of the microchannel walls, are considered as temperature-dependent functions compared with the isothermal case. Additionally, we show that the volumetric flow rate is drastically influenced when the zeta potential varies with temperature.     

Predictions of the gas–liquid flow in wet electrostatic precipitators

Based on Computational Fluid Dynamics (CFD), the present paper aims to simulate several important phenomena in a wet type ESP from the liquid spray generation to gas-droplet flow in electric field. A single passage between the adjacent plates is considered for the simulation domain. Firstly, the electric field intensity and ion charge density are solved locally around a corona emitter of a barbed wire electrode, which are applied to the entire ESP using periodic conditions. Next, the Euler–Lagrange method is used to simulate the gas-droplet flow. Water droplets are tracked statistically along their trajectories, together with evaporation and particle charging. Finally, the deposition density on the plate is taken as the input for the liquid film model. The liquid film is simulated separately using the homogenous Eulerian approach in ANSYS-CFX. In the current case, since the free surface of the thin water film is difficult to resolve, a special method is devised to determine the film thickness.As parametric study, the variables considered include the nozzle pressure, initial spray spreading patterns (solid versus hollow spray) and plate wettability. The droplet emission rate and film thickness distribution are the results of interest. Main findings: electric field has strong effect on the droplet trajectories. Hollow spray is preferred to solid spray for its lower droplet emission. The liquid film uniformity is sensitive to the plate wettability.     

沉降过程的扩散机理及其数学表达式

本文分析了固液二相流体中的扩散机理，并从水流的紊动出发，指导出固体颗粒在二维水流中分布的理论公式。     

A phase field model in electrowetting and related phenomena

The term electrowetting is commonly used for some techniques to change the shape and wetting behaviour of liquid droplets by the application of electric fields and charges. We developand analyze a model for electrowetting that combines the Navier-Stokes system for fluid flow, a phase-field model of Cahn-Hilliard type for the movement of the interface, a charge transport equation, and the potential equation of electrostatics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)