Collaborative research: Particle Dynamics in Viscous Shear Flows

1335781 PI：Ingber1335907 PI：悬浮在粘性剪切流中的刚性颗粒的基本流变学仍然没有得到很好的理解，特别是，实验观察到的不可逆性在名义上是一个可逆的流动的起源是不清楚的。这个合作项目的主要目标是确定的不可逆性的主要原因，量化的不可逆性，并确定如何最好地将不可逆性纳入悬浮液流的介观模型。虽然存在由短程相互作用引起的不可逆性的一般概念，但这些相互作用的确切性质和大小是未知的，并且在许多情况下，各种粗糙度模型或排斥力或多或少以特设方式应用。只要这个基本的研究问题仍然没有答案，就没有完全令人满意的方法来制定任何类型的流变模型。该项目将试图确定，对不可逆转性的普遍处理必须取决于规模。对于相对较大的颗粒（大于100微米），悬浮液流不可逆性的主要原因通常是表面粗糙度。当颗粒尺寸减小到100微米以下时，假设不可逆性的主要原因从表面粗糙度转变为非流体动力学静态力，该静态力可包括诸如静电力和货车范德华力的力。此外，该项目将建立不可逆的颗粒迁移与剪切流的非线性测量呈线性关系。这些假设的建立将对目前缺乏普适性的流变学模型产生强烈的影响。拟议中的研究直接影响科学和工程的几个关键领域，对日常生活有许多影响。悬浮液流在各种各样的不断发展的技术中是重要的，包括先进的材料处理、色谱法、封装、微流体、通过水力压裂的二次采油、二氧化碳封存以及沉积物、污染物和浆料的运输，仅举几例。在过去的几年里，已经开发了几种流变模型，以帮助工程师开发涉及悬浮液的有效工艺。尽管这些模型在确定稳态浓度分布方面相对成功，但它们未能模拟瞬态。该研究将弥补现有模型的不足。研究工作将辅之以强有力的教育和外联部分。

1335781PI: Ingber1335907PI: VorobieffThe fundamental rheology of rigid particles suspended in viscous shear flows is still not well understood, and in particular, the origins of experimentally observed irreversibility in what is nominally a reversible flow are unclear. The main objectives of this collaborative project are to identify the primary causes of the irreversibility, to quantify the irreversibility, and to determine how best to include irreversibility into mesoscopic models of suspension flows. While there exists a general notion of irreversibility being caused by short-range interactions, the exact nature and magnitude of these interactions is unknown and, in many cases, various roughness models or repulsive forces are applied more or less in an ad hoc manner. As long as this fundamental research question remains unanswered, there is no fully satisfactory way to formulate any type of rheological model. The project will attempt to establish that a universal treatment of irreversibility must be scale-dependent. For relatively large particles (greater than, say,100 microns), the major cause of irreversibility in suspension flows is typically surface roughness. As the size of the particles decreases below 100 microns, it is hypothesized that there exists a transition in the major cause of irreversibility from surface roughness to nonhydrodynamic static forces which may include forces such as electrostatic and van der Waals forces. Furthermore, the project will establish that irreversible particle migration scales linearly with a measure of nonlinearity of the shear flow. The establishment of these hypotheses will have a strong impact on rheological models, which currently lack universality. The proposed research directly affect several key areas of science and engineering, with many implications for everyday life. Suspension flows are important in a wide variety of evolving technologies including advanced materials processing, chromatography, encapsulation, microfluidics, secondary oil recovery by hydraulic fracturing, carbon-dioxide sequestration, and the transport of sediments, contaminants, and slurries, to name a few. Several rheological models have been developed over the past several years to help engineers develop effective processes involving suspensions. Although these models have been relatively successful in determining steady state concentration profiles, they fail to model the transient states. This research will remediate the shortcomings of the existing models. The research effort will be complemented with a strong educational and outreach component.