Sphere-Sphere and Sphere-Surface Interactions in Viscoelastic Fluids

粘弹性流体中的球-球和球-表面相互作用

• 批准号: 0851552
• 负责人: Ronald Phillips
• 金额: $ 30万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0851552&HistoricalAwards=false
• 关键词: Sphere; Surface; Interactions; Viscoelastic; Fluids

0851552R. PhillipsThe important problem of how particles suspended in non-Newtonian fluids interact with each other and with nearby surfaces remains relatively unstudied in comparison with similar problems involving Newtonian fluids. These interactions between particulates in polymer solutions and melts can result in aggregation, chaining, and movement toward or away from the walls bounding a flow. Even such seemingly simple questions such as whether two spheres sedimenting along their line-of-centers will move together to form a doublet, or move apart, remain unanswered. Similarly, the limited published experimental data on the rate of fall of a sphere perpendicular to (i.e., toward or away from) a flat surface disagrees qualitatively with theoretical predictions. These two problems, the axisymmetric sedimentation of two spheres and the movement of a sphere normal to a planar surface, are of practical importance in applications such as the processing of composite materials, the use of proppant particles in oil recovery, and the application of "lab-on-a-chip" microelectronic devices. They are also ideal candidates for fundamental research, because their axisymmetric geometry makes them accessible to both experimental measurement and numerical calculations. In the proposed research, particle image velocimetry (PIV) will be used to measure velocity fields in planar regions around two sedimenting spheres and spheres moving normal to interfaces. Particle velocities will also be measured directly, by using charge couple device (CCD) cameras. Experiments will be performed in polymer solutions that exhibit elasticity with negligible shear thinning (i.e., Boger fluids), solutions that are strongly shear thinning but exhibit very weak elasticity, and solutions that are both strongly elastic and shear thinning. The sizes and densities of the spherical particles will be such that the Deborah numbers are of order unity, but the Reynolds and Stokes numbers will be small, isolating the effects of the non-Newtonian rheology relative to inertia. Numerical calculations of viscoelastic flow around spherical particles will be performed by an approach that accounts for the hyperbolic nature of the constitutive equations and the elliptic nature of the momentum conservation equations. The proposed methods are capable of resolving the stress boundary layers and regions of severe polymer stretching that are present in viscoelastic flow around particles at finite Deborah numbers. Preliminary calculations show the formation of a negative wake, or region where the fluid moves in the direction opposite to that a sedimenting sphere, in flows with strong elasticity as well as shear thinning. The formation of a negative wake is qualitative agreement with experimental measurements of two-sphere sedimentation performed by PIV.Intellectual MeritThe proposed work consists of carefully chosen experiments in the simplest possible geometries that are still relevant to nearly all flows of non-Newtonian suspensions. These experiments will involve quantitative measurements of velocity profiles that can be compared quantitatively to calculations done by our group and by others. The students involved will gain an appreciation for both experimental and computational work, as well as the importance of establishing a close connection between these two avenues of research when dealing with complicated materials.Broader ImpactThis research will provide an excellent educational opportunity for graduate and undergraduate students. It has applications in a wide range of areas, including developing new composite and nanocomposite materials, improving oil recovery, and designing new "lab-on-a-chip" microdevices. Undergraduate students will be recruited from underrepresented groups, both to help with the research and to create instructional materials to be used in classroom teaching

0851552R。与涉及牛顿流体的类似问题相比，悬浮在非牛顿流体中的颗粒如何相互作用以及与附近表面相互作用的重要问题仍然相对未被研究。聚合物溶液和熔体中的颗粒之间的这些相互作用可导致聚集、链接和朝向或远离界定流动的壁的移动。即使是这样看似简单的问题，例如两个球体沿着它们的中心线沿着沉降，是否会移动到一起形成一个双重体，或者分开，仍然没有答案。同样，关于垂直于（即，朝向或远离）平坦表面与理论预测定性地不一致。这两个问题，即两个球体的轴对称沉降和球体垂直于平面表面的运动，在诸如复合材料的加工、在石油开采中使用支撑剂颗粒以及“芯片实验室”微电子器件的应用等应用中具有实际重要性。它们也是基础研究的理想候选者，因为它们的轴对称几何形状使它们可以进行实验测量和数值计算。 在这项研究中，粒子图像测速技术（PIV）将被用来测量两个沉降球和垂直于界面运动的球周围的平面区域的速度场。粒子速度也将直接测量，通过使用电荷耦合器件（CCD）相机。实验将在表现出弹性且剪切稀化可忽略不计的聚合物溶液中进行（即，Boger流体），强剪切稀化但表现出非常弱的弹性的溶液，以及强弹性和剪切稀化两者的溶液。球形颗粒的尺寸和密度将使得Deborah数为单位阶数，但雷诺数和斯托克斯数将较小，从而隔离相对于惯性的非牛顿流变学的影响。 球形颗粒周围的粘弹性流动的数值计算将进行的方法，占双曲线性质的本构方程和椭圆性质的动量守恒方程。所提出的方法是能够解决的应力边界层和严重的聚合物拉伸，存在于颗粒周围的粘弹性流动在有限的德博拉数的区域。初步计算表明，在具有强弹性和剪切变稀的流动中，形成负尾流，或流体沿与沉降球相反的方向移动的区域。负尾流的形成是定性的协议与实验测量的两个球体的沉降进行PIV。智力MeritThe建议的工作包括精心挑选的实验中最简单的可能的几何形状，仍然是相关的几乎所有的非牛顿悬浮液流。这些实验将涉及速度分布的定量测量，可以与我们小组和其他人所做的计算进行定量比较。参与的学生将获得对实验和计算工作的赞赏，以及在处理复杂材料时建立这两种研究途径之间密切联系的重要性。更广泛的影响这项研究将为研究生和本科生提供一个极好的教育机会。它在广泛的领域中有应用，包括开发新的复合材料和纳米复合材料，提高石油采收率，以及设计新的“芯片实验室”微器件。本科生将从代表性不足的群体中招募，既帮助研究，又创建用于课堂教学的教学材料