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An experimental study of pressure- and electroosmotically-driven flows in microchannels with surface modifications.

机译：具有表面修饰的微通道中压力驱动和电动力驱动的流动的实验研究。

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摘要

Researchers investigating pressure-driven flows within microchannels have reported a discrepancy with classical theory. These discrepancies were attributed to various reasons; notably entrance effects, electroviscous effects, early transition to turbulence, surface roughness effects, etc. These measurements were all performed using bulk flow measurement techniques such as pressure drop and flow rate measurements. To investigate if deviations from classical theory do exist, the friction factor obtained from the current study was compared to classical theory for microchannels with a characteristic size of 300mum. The determination of the friction factor in this study differs from other researchers as it is derived from local measurements of the velocity profile using the Molecular Tagging Velocimetry (MTV) technique. This is the first time that a local measurement of the velocity profile has been used to derive the friction factor. Local measurements are advantageous as entrance effects do not affect it and it does not suffer from the high order dependence on diameter (D4) when relating pressure drop to volume flow rate. The microchannels used in this study were coated with polymer brushes (HEMA) and octadecyl-trichlorosilane (OTS) to investigate if the added hydrophobicity of these coatings would affect the pressure-driven flow.; The second part of this study relates to electroosmotically-driven flows within microchannels. Electroosmotically-driven flows are of interest as pressure-driven flows become increasingly ineffective in transporting fluid due to the increase in surface to volume ratios in smaller microchannels. The electroosmotic velocity's dependence on temperature and the applied electric potential was studied using a simultaneous velocity and temperature measurement technique (Molecular Tagging Velocimetry & Thermometry, MTV&T). The estimation of the electroosmotic velocity based only on the Helmholtz-Smoluchowski equation was found to be inadequate due to the presence of Joule heating and showcases the need for a simultaneous local measurement of both the velocity and temperature to resolve the flow physics. This local measurement technique is also used to obtain local zeta potential (zeta) measurements of the different surfaces. Zeta potential information is important in designing microfluidic devices to improve mixing characteristics within microchannels. An added capability of the measurement technique to reveal zeta potential dependence on temperature is also presented. To further our understanding of the spatio-temporal evolution of temperature within the microchannel during electroosmosis, a numerical simulation (FLUENT) was employed with boundary conditions similar to our experimental studies.
机译：研究微通道内压力驱动流动的研究人员报告了与经典理论的差异。这些差异归因于各种原因。尤其是入口效应，电粘性效应，湍流的早期过渡，表面粗糙度效应等。这些测量都是使用大流量测量技术（如压降和流量测量）进行的。为了研究是否存在与经典理论的偏差，将当前研究获得的摩擦系数与特征尺寸为300μm的微通道的经典理论进行了比较。本研究中摩擦系数的确定与其他研究人员不同，因为它是使用分子标记测速技术（MTV）从速度分布的局部测量得出的。这是第一次使用速度曲线的局部测量来得出摩擦系数。局部测量是有利的，因为入口效应不会对其产生影响，并且在将压降与体积流率相关时，它不会受到高度依赖于直径（D4）的影响。本研究中使用的微通道涂有聚合物刷（HEMA）和十八烷基三氯硅烷（OTS），以研究这些涂层增加的疏水性是否会影响压力驱动的流动。这项研究的第二部分涉及微通道内的电渗流。由于在较小的微通道中表面积与体积之比的增加，压力驱动的流动在输送流体方面变得越来越无效，因此电渗流受到关注。使用同时速度和温度测量技术（分子标记测速与测温，MTV＆T）研究了电渗速度对温度和施加电势的依赖性。由于焦耳热的存在，仅基于Helmholtz-Smoluchowski方程对电渗速度的估计是不充分的，并且表明需要同时对速度和温度进行局部测量以解决流动物理问题。该局部测量技术还用于获得不同表面的局部zeta电位（zeta）测量。 Zeta电位信息对于设计微流控设备以改善微通道内的混合特性非常重要。还介绍了测量技术揭示zeta电位对温度的依赖性的附加功能。为了进一步了解电渗过程中微通道内温度的时空演化，采用了与我们的实验研究相似的边界条件下的数值模拟（FLUENT）。

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  • 作者

    Lum, Chee Leong.;

  • 作者单位

    Michigan State University.;

  • 授予单位 Michigan State University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 180 p.
  • 总页数 180
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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