Axial Dispersion Due to Shear-induced Diffusion in Suspensions

1234500 PI：了解悬浮力学是至关重要的设计和表征的新的和发展中的技术，因为颗粒负载的材料出现在无数的流体系统，例如颗粒增强塑料，胶体材料的化学和生物检测，疾病识别和药物输送，细胞悬浮液，乳液和建筑材料。由于颗粒浓度分布与材料流变性的耦合，对常见悬浮液流动的定量理解变得复杂。特别地，典型的悬浮液是非牛顿的，因为它们表现出有效粘度和法向应力差对颗粒的局部浓度和剪切或拉伸速率的依赖性。此外，由于剪切引起的迁移现象，流中的颗粒分布通常在平行于和横向于平均流动方向的方向上演变。输送过程的这一特征既影响颗粒塞的分散，又影响悬浮液的平均运动速度。我们最近取得了进展，对表征理论上的轴向分散在稀悬浮液中，其中负责分散的波动发生作为剪切引起的迁移/扩散的颗粒的结果。最显著的是，对于典型的流动条件，当剪切诱导扩散效应显著时，颗粒团的有效轴向分散减少。此外，有效轴向弥散度与平均流速成线性比例，并且作为管道或通道半径的三次方，这两个特征不同于传统的布朗运动驱动的轴向弥散。提案的重点集中在三个主要问题上：（i）对于单分散悬浮液的轴向扩散是由剪切诱导的迁移/扩散驱动的波动产生的情况，轴向分散思想的概括，（ii）分析剪切诱导的扩散对双分散悬浮液流中的传输和颗粒分离的影响，以及（iii）分析具有非均匀横截面形状的通道的轴向色散过程，这是许多微器件的典型特征。在每种情况下，都需要将颗粒的分布与传输特性（有效扩散率、有效粘度、法向应力差等）相结合。实验将补充建模。这些结果将适用于新的应用，包括悬浮液或检测方法，其中一团特殊设计的颗粒被注入到一个流中。许多常见的材料是悬浮液，悬浮液是指分布在液体中的固体颗粒（或其他种类的颗粒）。这些材料在工业上使用，并且通常用于家庭、食品、药品等。通常需要将另外的颗粒混合到悬浮液中，或者改变悬浮液的性质（例如，材料流动的容易程度），或向混合物中添加功能在一些实施例中，可以通过添加药物（例如添加药物）来检测流体中的有害颗粒，或者添加可以检测流体中的有害颗粒的物体（例如可以识别或捕获致病细胞的小传感器）来检测流体中的有害颗粒。在这些情况下，有必要定量和定性地了解这种混合是如何发生的，以及添加剂如何在悬浮液中重新分布。虽然有复杂的理论和数值工具，这样的分子溶质的混合，有少得多的了解宏观粒子的传播和分布。我们将使用理论，建模和实验来解决这些问题，并为理解这些分散，即扩散过程制定定量指导方针。

1234500PI: StoneUnderstanding suspension mechanics is crucial to the design and characterization of new and developing technologies since particle-laden materials occur in a myriad of fluid systems, e.g. particle-reinforced plastics, colloidal materials for chemical and biological detection, disease identification and drug delivery, cellular suspensions, emulsions, and building materials. Quantitative understanding of common suspension flows is complicated by the coupling of the particle concentration distribution to the rheology of the material. In particular, typical suspensions are non-Newtonian as they exhibit dependence of the effective viscosity and normal stress differences on both the local concentration of particles and the shear or extension rate. Furthermore, the particle distribution in a flow typically evolves in directions both parallel and transverse to the mean flow direction due to the phenomenon of shear-induced migration. This feature of the transport process affects both the dispersion of a plug of particles, and the average speed of motion of the suspension. We have recently made progress towards characterizing theoretically axial dispersion in a dilute suspension, where the fluctuations responsible for the dispersion occur as a consequence of shear-induced migration/diffusion of the particles. Most significantly, for typical flow conditions, the effective axial dispersion of a bolus of particles is reduced when shear-induced diffusion effects are significant. In addition, the effective axial dispersivity scales linearly with the average flow speed and as the third power of the pipe or channel radius, both features differ from the traditional Brownian motion-driven axial dispersion. The focus of the proposal centers on three main problems: (i) the generalization of axial dispersion ideas for the case where axial spreading of a monodisperse suspension is produced by fluctuations that are driven by shear-induced migration/diffusion, (ii) analyzing the influence of shear-induced diffusion on transport and particle separation in bidisperse suspension flows, and (iii) analyzing the axial dispersion process for channels with non-uniform cross-sectional shapes as is typical of many microdevices. In each case it is necessary to couple the distribution of particles to the transport properties (effective diffusivity, effective viscosity, normal stress differences, etc.). Experiments will complement the modeling. The results will be applicable to new applications involving suspensions or detection methods whereby a bolus of specially designed particles is injected into a flow.Many common materials are suspensions, which refers to solid particles (or other kinds of particulates) distributed in a liquid. These materials are used industrially and are in common uses in households, food products, pharmaceuticals, etc. Often it is necessary to blend additional particles into a suspension, either to modify the properties of the suspension (e.g. how easily the material flows), or to add a functionality to the mixture (e.g. adding a drug), or to add objects that may detect harmful particles in the flow (e.g. small sensors that might identify or capture pathogenic cells). In these cases it is necessary to understand quantitatively and qualitatively how this mixing takes places, and how the additive is redistributed in the suspension. Although there are sophisticated theoretical and numerical tools for such mixing of molecular solutes, there is much less known about the spreading and distribution of macroscopic particles. We will address these questions using theory, modeling and experiments, and develop quantitative guidelines for understanding these dispersive, i.e. spreading, processes.