Collaborative research: Particle Dynamics in Viscous Shear Flows

1335781圆周率：英格伯1335907圆周率：沃罗比耶夫悬浮在粘性剪切流动中的刚性颗粒的基本流变学仍不清楚，尤其是在名义上可逆的流动中，通过实验观察到的不可逆性的起源尚不清楚。该合作项目的主要目标是确定不可逆性的主要原因，量化不可逆性，并确定如何最好地将不可逆性纳入悬浮流的介观模型。虽然存在一个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尚不清楚，在许多情况下，各种粗糙模型或排斥力或多或少以一种特别的方式应用。只要这个基础研究问题仍未得到回答，就没有完全令人满意的方法来建立任何类型的流变学模型。该项目将试图确立，不可逆性的普遍处理必须依赖于规模。对于相对较大的颗粒(比方说大于100微米)，悬浮流动中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存在从表面粗糙到非流体动力静力的转变，其中可能包括静电力和范德华力。此外，该项目将建立不可逆粒子迁移尺度与剪切流的非线性度的线性关系。这些假说的建立将对目前缺乏普适性的流变模型产生强烈影响。拟议中的研究直接影响到科学和工程的几个关键领域，并对日常生活产生了许多影响。悬浮流在各种不断发展的技术中都很重要，包括先进的材料处理、层析、胶囊化、微流体、水力压裂二次采油、二氧化碳封存以及沉积物、污染物和泥浆的运输等。在过去的几年里，已经开发了几个流变模型来帮助工程师开发涉及悬浮液的有效工艺。虽然这些模型在确定稳态浓度分布方面取得了相对成功的结果，但它们不能对暂态进行建模。本研究将弥补现有模型的不足。这项研究工作将辅之以强有力的教育和宣传部分。

1335781 PI: Ingber 1335907 PI: Vorobieff The 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.