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

摘要-0411634智力优点。涉及固体颗粒流动的过程在自然界和地球上都是普遍存在的（滑坡、行星环等）.和工业（制药，食品，化学加工工业），尽管对它们的行为的预测性理解仍然是一个难以捉摸的目标。 在所提出的努力中特别感兴趣的是涉及涂覆有粘性流体薄层的颗粒的系统-即，湿固体这样的颗粒系统在广泛的应用中被发现，包括流化床造粒、药物混合、花粉运输、过滤等。已知这样的系统显示出通常不被它们的干燥对应物显示出的特性，即存在颗粒附聚物。团聚的形成，重排，增长和破碎的预测知识是湿固工艺的合理设计的关键因素，虽然这样的预测工具是目前不可用的。 目前的努力旨在解决上述需求，特别关注润湿颗粒之间发生的粘性（动态）效应，与润湿系统的毛细（静态）效应和完全浸没系统的粘性效应相比，这是相对未开发的。理论，实验和离散粒子模拟的结合将被用来回答以下与湿固体相关的关键问题：（一）当两个“自由”粒子碰撞时，会形成团聚体吗？(ii)如果没有形成凝聚体，那么液体层对碰撞后粒子运动的影响是什么？(iii)如果凝聚物确实形成了，那么与第三个粒子碰撞的结果是什么？(iv)这些微观物理学如何影响颗粒和气固系统的宏观（连续）行为？更具体地说，实验和基础理论的润滑，毛细管力和固体力学的组合将用于开发小团聚体的坚持/反弹和破碎标准。该理论只要求溶液具有可测量的固体和液体性质。 为了将微观物理与宏观行为联系起来，微观物理理论将被纳入离散粒子模拟。液体层对连续体量如应力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，离散颗粒模拟也将进行一个特定的气固操作，即流化床造粒（或扩大），在努力描述一些非直观的行为，在这样的系统中观察到。 这项工作将是PI（克莉丝汀教授）和联合PI（Rob Davis教授）之间的合作，他们在与颗粒流相关的理论、实验和模拟方面具有广泛的背景。这项工作的广泛影响包括：（i）对湿颗粒系统有更基本的了解，（ii）对研究生进行颗粒技术领域的培训，这已被确定为国家的需要[1-3]，以及（iii）与技术界分享所学到的信息（通过演讲和同行评议的出版物）和学生社区（通过纳入课程，培训计划和推广）。

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).