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Laminar and turbulent flow of a liquid through channels with superhydrophobic walls exhibiting alternating ribs and cavities.

机译：液体的层流和湍流通过具有超疏水壁的通道呈现出交替的肋和腔。

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摘要

There is significant interest in reducing the frictional resistance that occurs along a surface in contact with a liquid. A novel approach to reducing the frictional resistance across a liquid-solid interface is the use of superhydrophobic surfaces. Superhydrophobic surfaces are created in this work by the use of micro-fabrication techniques where systematic roughness is fabricated on a substrate surface which is subsequently treated with a hydrophobic coating. This work reports an experimental study of superhydrophobic surfaces used to reduce drag in both laminar and turbulent channel flows.;In the laminar flow regime reductions in frictional resistance greater than 55% were measured in microchannels consisting of superhydrophobic walls. The reduction in frictional resistance for laminar flow in microchannels with superhydrophobic walls was shown to be dependent on the rib/cavity orientation, with greater reduction achieved when the ribs/cavities were aligned parallel with the direction of the flow. Also, the ratio of the cavity width to the combined rib/cavity pitch and the ratio of the combined rib/cavity pitch to the microchannel hydraulic diameter exercise influence on the frictional resistance. The condition when the flowing liquid was allowed to completely "wet" the cavities was also explored. Generalized expressions enabling prediction of the classical friction factor-Reynolds number product as a function of the relevant governing parameters were also developed.;The influence of superhydrophobic surfaces in turbulent flow was explored in macrochannels (hydraulic diameter≈ 8.5 mm) using particle imaging velocimetry (PINT). For the turbulent flow regime the time-averaged velocity profiles revealed no discernible slip velocity at the superhydrophobic wall. However, the results did show that the superhydrophobic surfaces exhibits an influence on the streamwise and wall-normal turbulence intensities, the turbulent shear stress, the total shear stress distributions, and the turbulence production in the channel. From the total shear stress distributions in the channel the coefficient of friction at the channel walls was determined. The results showed that for the superhydrophobic surface with ribs and cavities oriented parallel to the flow direction a reduction in the coefficient of friction as high as 16% was achieved compared to a smooth wall channel. Superhydrophobic surfaces with ribs and cavities oriented transverse to the flow direction showed a modest increase in the coefficient of friction. Differential pressure measurements in the turbulent flow channel were also acquired and used to calculate the channel average friction factor.
机译：降低在与液体接触的表面上产生的摩擦阻力引起了极大的兴趣。减少液-固界面上的摩擦阻力的一种新颖方法是使用超疏水表面。在这项工作中，通过使用微细加工技术创建了超疏水表面，其中在基材表面上制备了系统粗糙度，然后用疏水性涂层对其进行处理。这项工作报告了用于减少层流和湍流通道流动阻力的超疏水表面的实验研究。在层流状态下，由超疏水壁组成的微通道测得的摩擦阻力降低幅度超过55％。在具有超疏水壁的微通道中，层流的摩擦阻力的减小显示出取决于肋/腔的方向，当肋/腔平行于流动方向排列时，摩擦阻力的减小更大。而且，腔宽度与肋/腔的组合节距的比以及肋/腔的组合的节距与微通道水力直径的比对摩擦阻力有影响。还探讨了允许流动的液体完全“润湿”型腔的条件。还开发了可预测经典摩擦因子-雷诺数乘积作为相关控制参数的函数的通用表达式。;使用颗粒成像测速仪（液压直径＆ap; 8.5 mm）在大通道中探索了超疏水表面对湍流的影响品脱）。对于湍流状态，时间平均速度曲线显示在超疏水壁上没有可辨别的滑移速度。然而，结果确实表明，超疏水表面对水流和壁面的湍流强度，湍流剪切应力，总剪切应力分布以及通道中的湍流产生影响。根据通道中的总剪切应力分布，确定通道壁处的摩擦系数。结果表明，对于肋和腔平行于流动方向定向的超疏水表面，与光滑的壁通道相比，摩擦系数降低了16％。肋和腔垂直于流动方向取向的超疏水表面显示出适度的摩擦系数增加。还获得了湍流通道中的压差测量结果，并用于计算通道平均摩擦系数。

著录项

  • 作者

    Woolford, Brady L.;

  • 作者单位

    Brigham Young University.;

  • 授予单位 Brigham Young University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 286 p.
  • 总页数 286
  • 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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