电渗驱动微泵设计初探

电渗驱动微泵是一种新型的微泵,具有输出压强高、流量可调范围宽、结构简单、无活动部件等特点,易与微通道热沉集成,构成微通道冷却系统,可用于集成电路的热管理.本文介绍了电渗驱动微泵的数学模型,利用PB方程来描述电渗流中电势和离子分布,讨论了背压与流速的关系,槽道宽度、工作液体温度、外加电压等参数对电渗泵性能的影响.     

新型双并联电渗微泵的制备与测试

设计了一个双并联电渗驱动泵,它由三条并联的主通道和叉指型电极两部分组成,其中每条主通道由若干个与电渗流形成方向成45°角的沟槽并联构成。通过选用ITO载玻片作为芯片基底并获得其最佳工艺参数,制作了带电极的PDMS-玻璃微流控芯片。最后对制作的电渗微泵进行测试,通过记录一段时间内单个主通道泵输送液体的体积,得出单个主通道的流速与微泵总流速。实验发现在5V内,微泵泵送液体的能力随着电压的增加而增大,微泵流速可以达到正常人体眼球房水生成速度,该结构在未来房水引流器件制作方面具有潜在的应用价值。     

含时滞的半主动系统动力学分析

对含时滞的半主动相对控制悬架系统进行了近似解析研究.首先建立了半主动相对控制1/4车体模型,进行了无量纲化处理,利用平均法建立了系统的近似解析解应该满足的四元代数方程组,然后利用数值方法进行了求解.随后通过MATLAB仿真得到了含时滞的半主动相对控制悬架系统的数值解,并且和近似解析解进行了比较,发现二者具有较好的符合精度,说明近似解析解的正确性.     

基于模拟退火算法的多孔介质三维重建

为了研究固相转换器内部流体的流动状态,将动态退火系数的模拟退火算法与基于改进的状态更新的随机重建方法相结合,提出一种对固相转换器这类多孔介质进行软件重建的三维随机重建策略.首先对显微CT采集得到的多孔介质图像进行处理,得到基于孔隙相与固体相的二值化图像,并将其作为参考模型;然后在保持多孔介质孔隙率不变的前提下对多孔介质进行重建,实现了对其采样、图像处理与重建的过程.实验结果表明,该策略可以提升重建速度与渗透率的精度,重建模型与参考模型的两点相关函数与孔隙分形维数有很好的一致性.     

基于热平衡算法的多孔材料吸水性仿真研究

为获取多孔材料最准确的吸水特性,在理想流体温度环境下,通过热平衡算法计算多孔材料吸水性并进行仿真研究.分析多孔材料内流动与传热影响,无量纲化处理流体速率,构建热平衡计算能量方程,明确热平衡模式下多孔材料固体和流体状态;组建一维多孔材料水分运动解析式,计算多孔材料吸水初始条件与上、下边界条件,得到多孔材料吸水模型,将吸水率运算当作非线性最小优化问题,求解多孔材料吸水模型参数,获得精确吸水性测量信息.在热平衡环境下对多孔材料单面浸泡、整体浸泡与真空饱和三种吸水状态进行仿真,结果表明:多孔材料在热平衡环境下孔隙率越高,毛细饱和含水率越大,毛细吸水系数与毛细饱和含水率呈线性正关联.     

基于响应面方法的波导介质层PBG结构滤波器的优化设计

在辛体系下利用精细积分对矩形波导纵向排列介质层PGB结构进行分析的基础之上,用响应面方法对滤波器进行了优化设计.采用棱单元对波导的横截面进行离散,然后导向哈密顿体系,运用基于黎卡提微分方程的精细积分求出一段介质层和一段空气层的出口刚度阵,再将两区段合并得到一个周期段的出口刚度阵,从而可对所有周期进行合并以对问题求解.在分析的基础上建立了滤波器的优化设计模型,利用响应面方法将目标函数和约束函数近似显式化,运用二次规划法对优化模型进行求解,得到了滤波性能最优的设计参数.算例表明本文方法是可行有效的.     

多孔介质孔隙结构的网络模型应用

本研究分别用毛细管束模型和网络模型对多孔介质的孔构型进行描述。为了克服毛细管束模型在反映真实结构存在的局限性 ,有必要发展更为精确的方法。在诸多的多孔介质模型中 ,网络模型经过多年的研究、发展 ,已经可以较好地实现对过程机理进行定量预测。进一步通过引入非线形分形理论 ,对复杂孔隙结构可望得到更为真实可靠的构型模型     

含阵列电极的硅基电泳芯片微管道性能的表征和分析

以含阵列电极的SOI硅基芯片与PDMS盖片制成的复合电泳芯片为对象,研究芯片电泳过程中芯片微管道的特殊表面电化学性质.实验采用电流监测法,利用溶液探针测试体系来表征微管道的电绝缘性,由于工艺缺陷或芯片长时间使用引起的绝缘层不同程度的损坏,导致在充液管道中产生的10-500μA的基底电流,这又导致不同程度焦耳热,进而导致电渗流无法稳定和芯片电泳过程无法正常进行.实验提出通过优化硅-PDMS电泳芯片的结构设计来避免和减小基体电流,同时采用以导热硅酯为介质的散热器对硅片试验体系进行散热,进一步减小焦耳热的影响以获得稳定的电渗流.在此基础之上,实验测得硅-PDMS微管道中的电渗迁移率为3.9×10-4 cm2/V·s,伏安曲线显示5 mmol硼砂缓冲中最大施加电压为260 V/cm;采用本文提出的复合芯片系统,分离FITC标记的精氨酸和苯丙氨酸混合样品,分离度达到3.14,柱效分别达到18 000和25 000.     

多孔介质孔隙模型及其应用——毛细管束模型

在多孔介质中许多物理化学行为均与其自身的孔隙结构构型密切相关 ,建立一种切实可行的孔隙模型将会对研究材料和化工过程多孔介质提供很大的帮助。毛细管模型是一种较为简单的实用孔隙模型 ,它可以通过使用毛细管压对多孔介质的浸渗和排空情况进行计算 ,也可以用于对多孔介质中的浸渗和排空过程进行定性的解释。针对在研项目 ,对毛细管束模型情况做一评述     

多孔介质孔隙结构的网络模型应用

本研究分别用毛细管束模型和网络模型对多孔介质的孔构型进行描述。为了克服毛细管束模型在反映真实结构存在的局限性,有必要发展更为精确的方法,在诸多的多孔介质模型中,网络模型经过多年的研究、发展,已经可以较好地实现对过程机理进行定量预测,进一步通过引入非线形分形理论,对复杂孔隙结构可望得到更为真实可靠的构型模型。     

Numerical analysis of non Newtonian fluid flow in a low voltage cascade electroosmotic micropump

In microfluidic devices, many fluids have non-Newtonian behaviors, especially biofluids. The viscosity of these fluids mostly depends on the shear rate. Sometimes the non-Newtonian fluids should be transferred by micropumps in lab-on-chip devices. Previous researchers investigated the flow rate in simple electroosmotic flow micropumps which have a simple channel geometry. In the present study, the effects of non-Newtonian properties of fluid in a low voltage cascade electroosmotic micropump are numerically investigated using the power law model. The micropump is modeled in two dimensional with one symmetric step and has a more complex geometry than previous studies. The numerical results show that, the non-Newtonian behavior of fluid affects flow rate in the micropump. The flow rate decreases if the fluid is dilatant. Also, it increases if the fluid is pseudoplastic. Moreover, the pressure which is needed to stop the electroosmotic flow rate in the micropump is calculated. Results show that, the back pressure has a slight change as the fluid has non-Newtonian behavior.     

Theoretical and numerical investigations of an electroosmotic flow micropump with interdigitated electrodes

In this work, an electroosmotic flow micropump is proposed and investigated using theoretical analysis and numerical simulations. The micropump comprises an array of interdigitated electrodes on the top and the bottom surfaces of a rectangular microchannel. Theoretical analysis and extensive numerical simulations are performed to predict the pressure-flow characteristics of the micropump. The results of the model and simulations are compared which show good agreement with each other. The effects of various geometrical parameters including spacing between a pair of electrodes, gap between adjacent pairs of electrodes, width and height of the electrodes, and width of the microchannel and operating parameter including applied voltage on the performance of the micropump in terms of flow and pressure capacity is investigated.     

Analysis of electroosmotic flow in a microchannel packed with microspheres

The electroosmotic flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called capillary model is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier–Stokes equation and the complete Poisson–Boltzmann equation. Then, using the volume-averaging method, the solution for the electroosmotic flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinetic wall effect is obtained by solving the modified Brinkman momentum equation. For the electroosmotic flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of the channel ends are considered. Based on the capillary model, the time-periodic oscillating electroosmotic flow in an open-ended microchannel in response to the application of an alternating electric field is obtained using the Greens function approach to the Navier–Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter flow, resulting in a new zero flow rate. Such induced backpressure associated with the counter flow in a closed-end microchannel is obtained analytically by solving the transient modified Brinkman momentum equation.     

A reduced-order model of the low-voltage cascade electroosmotic micropump

In the present investigation, we have derived an efficient reduced-order model of the low-voltage cascade electroosmotic micropump. This model can be combined with the equivalent circuit model of straight microchannels to construct a complete model for a microfluidic device, which can be employed to implement modern control schemes. To demonstrate the efficiency of the reduced-order model we employ it to estimate the zeta potentials of many subchannels in the micropump cascade using velocity measurements, which is a preliminary step to the implementation of modern control schemes. It is found that a conjugate gradient procedure employing the reduced-order model estimates accurately the zeta potential variation in the subchannels, which may be caused by adhesion of biomolecules, even with noisy velocity measurements.     

电渗微泵的生理溶液渗透特性研究

介绍了一种电渗微泵的结构及其驱动原理,研究了其对不同生理溶液的渗透特性。模拟眼内房水引流装置,利用电渗微泵对三种生理溶液进行测试,通过改变电压,测试定量体积的溶液,记录时间得出相应流速,用Origin Proporable软件对数据拟合得出压电流速曲线,结果表明电压对液体流动速度的影响成正比。人眼可承受最大5 V电压,此时该测试微泵传输液体流量每分钟可达到十几微升,通过分析5 V以内微泵对溶液的渗透性能,结合正常眼内房水引流速度,确定合理的驱动电压设计值,这将对未来制作实际可用的房水引流装置和器件产生指导意义。     

Equivalent electrical network for performance characterization of piezoelectric peristaltic micropump

Utilizing an electronic–hydraulic analogy, this study develops an equivalent electrical network of a piezoelectric peristaltic micropump which has not been modeled the whole system operation completely by computational fluid dynamics (CFD) or equivalent electrical network so far due to its excessive complicated structure. The validity of the proposed model is verified by comparing the simulation results obtained using the SPICE (simulation program with integrated circuit emphasis) software package for flow rate spectrum and its maximum state of a typical micropump with the experimental observations for two working fluids, namely DI water and blood. The simulation results predict a maximum flow rate frequency and flow rate of 280 Hz and 43.23 μL/min, respectively, for water, and 210 Hz and 24.12 μL/min for blood. The corresponding experimental results are found to be 300 Hz and 41.58 μL/min for water and 250 Hz and 23.75 μL/min for blood. The relatively poorer agreement between the two sets of results when using blood as the working fluid is thought to be the result of the non-Newtonian nature of blood, which induces a more complex, non-linear flow behavior within the micropump. Having validated the proposed model, the equivalent network is used to perform a systematic analysis of the correlation between the principal micropump design parameters and operating conditions and the micropump performance. The results confirm the validity of the equivalent electrical network model as the first microfluidic modeling tool for optimizing the design of peristaltic micropumps and for predicting their performance.     

Fluid flow through porous and nanoporous media within the prisme of extended thermodynamics: emphasis on the notion of permeability

The study of fluid flows through porous and nanoporous media is important in many natural and industrial situations. One relevant parameter is the permeability of the porous material. An original approach is proposed within the prism of Extended Irreversible Thermodynamics. More specifically, the system fluid–solid matrix is modelled by a two-component mixture and the permeability is obtained after calculating the seepage velocity and comparison with Darcy’s law. An explicit analytical expression of the permeability coefficient is proposed and discussed. The analysis is restricted to one-dimensional situations and incompressible fluids. The validity of the model is checked by calculating the flow rate through cylindrical nano pores: comparison with experimental data shows a good agreement.     

Electroosmotic control of width and position of liquid streams in hydrodynamic focusing

This paper presents theoretical and experimental investigations on electroosmotic control of stream width in hydrodynamic focusing. In the experiments, three liquids (aqueous NaCl, aqueous glycerol and aqueous NaCl) are introduced by syringe pumps to flow side by side in a straight rectangular microchannel. External electric fields are applied on the two aqueous NaCl streams. Under the same inlet volumetric flow rates, the applied electric fields are varied to control the interface positions and consequently the width of the focused aqueous glycerol stream. The electroosmotic effect on the width of the aqueous glycerol is measured using fluorescence imaging technique. The electroosmotic effect under different flow rates, different viscosity, and aspect ratio are investigated. The results indicate that the electroosmotic effect on the pressure-driven flow becomes weaker with the increase in flow rates, viscosity ratio or aspect ratio of the channel. The measured results of the focused width of the non-conducting fluid agree well with the analytical model.