Micro-Level and Macro-Level Flow Mechanics of Wet Granular Media

摘要- 0411634知识价值。涉及固体颗粒流动的过程在自然界（山体滑坡、行星环等）和工业（制药、食品、化学加工工业）中无处不在，尽管对其行为的预测性理解仍然是一个难以捉摸的目标。在提出的努力中，特别感兴趣的是涉及涂有薄层粘性流体（即湿固体）的颗粒的系统。这种颗粒系统在广泛的应用中被发现，包括流化床造粒，混合药物，花粉运输，过滤等。众所周知，这种系统显示出干燥系统通常不表现出的特征，即颗粒团块的存在。关于团聚形成、重排、生长和破裂的预测知识是合理设计湿固过程的关键因素，尽管目前还没有这样的预测工具。目前的工作旨在解决上述需求，特别关注湿润颗粒之间发生的粘性（动态）效应，与湿润系统的毛细（静态）效应和完全浸入系统的粘性效应相比，这是相对未被探索的。理论、实验和离散粒子模拟的结合将用于回答以下与湿固体相关的关键问题：(i)当两个“自由”粒子碰撞时会形成凝聚体吗？（ii）如果未形成凝聚体，液体层对碰撞后粒子运动的影响是什么？（iii）如果确实形成团块，与第三个粒子碰撞的结果是什么？（iv）这些微观层面的物理如何影响颗粒和气固系统的宏观层面（连续体）行为？更具体地说，实验与基于润滑、毛细力和固体力学的基础理论相结合，将用于制定小团聚体的粘/弹和破裂标准。该理论只要求溶液具有可测量的固体和液体性质。为了将微观层面的物理与宏观层面的行为联系起来，微观物理理论将被纳入离散粒子模拟。液体层对应力等连续量的影响将通过对颗粒材料的简单剪切流的检查来评估。此外，还将对特定的气固操作进行离散粒子模拟，即流化床造粒（或扩大），以努力描述在此类系统中观察到的一些非直观行为。这项工作将是PI （Christine Hrenya教授）和副PI （Rob Davis教授）之间的合作，他们在与颗粒流动相关的理论，实验和模拟方面具有广泛的背景。更广泛的影响。这项工作的更广泛影响包括以下方面：(i)对湿颗粒系统有更深入的了解，（ii）培养颗粒技术领域的研究生，这已被确定为国家需要[1-3]，以及（iii）与技术界（通过演讲和同行评审的出版物）和学生界（通过纳入课程、培训计划和外展）共享所学信息。

ABSTRACT - 0411634Intellectual Merit. Processes involving the flow of solid particles are ubiquitous in bothnature (landslides, planetary rings, etc.) and industry (pharmaceuticals, food products, chemical process industries), though a predictive understanding of their behavior remains an elusive goal. Of particular interest in the proposed effort are systems involving particles coated with a thin layer of viscous fluid - i.e., wet solids. Such particulate systems are found in a wide range of applications, including fluidized-bed granulation, mixing of pharmaceuticals, pollen transport, filtration, etc. Such systems are known to display characteristics that are typically not exhibited by their dry counterparts, namely the presence of particle agglomerates. A predictive knowledge of agglomeration formation, rearrangement, growth, and break-up is a key element in the rational design of wet-solid processes, though such a predictive tool is not currently available. The current effort aims to address the aforementioned need, with a particular focus on viscous (dynamic) effects occurring between wetted particles, which are relatively unexplored as compared to the capillary (static) effects of wetted systems and viscous effects of fully-immersed systems. A combination of theory, experiments, and discrete-particle simulations will be used to answer the following critical questions associated with wet solids: (i) Will an agglomerate form when two "free" particles collide? (ii) If an agglomerate is not formed, what is the impact of the liquid layer on the post-collisional particle motion? (iii) If an agglomerate does form, what is the result of a collision with a third particle? (iv) How do these micro-level physics impact the macro-level (continuum) behavior of both granular and gas-solid systems? More specifically, a combination of experiments and fundamental theory based on lubrication, capillary forces, and solid mechanics will be used to develop stick/bounce and breakup criteria for small agglomerates. The theory will require only measurable solid and liquid properties for solution. To bridge this micro-level physics with macro-level behavior, the microphysical theory will be incorporated into discrete-particle simulations. The effect of the liquid layer on continuum quantities like stress will be assessed via an examination of simple shear flow of a granular material. Furthermore, discrete-particle simulations will also be carried out for a specific gassolid operation, namely fluidized-bed granulation (or enlargement), in an effort to describe some non-intuitive behavior observed in such systems. This work will be a collaboration between the PI (Prof. Christine Hrenya) and the co-PI (Prof. Rob Davis), who have extensive background in the theoretical, experimental, and simulation aspects associated with particulate flows.Broader Impacts. The broader impacts of the work include the following: (i) a morefundamental understanding of wetted particulate system, (ii) training of graduate students in the area of particle technology, which has been identified as a national need [1-3], and (iii) sharing of learned information with both the technical community (via presentations and peer-reveiwed publications) and the student community (via incorporation into coursework, training programs, and outreach).