Bridging the Scales of Wetted Particulate Flows: Experiment, Theory, and Simulation

CBET-0754825，DavisIntellectual Merit。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、雪崩、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。特别感兴趣的是，在拟议的努力涉及系统的颗粒涂有一层薄薄的粘性流体？也就是说，湿固体这样的系统在广泛的应用（流化床造粒、药物混合、花粉运输、过滤等）中被发现，并且已知显示出与它们的干燥对应物不同的特征，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。初步实验显示两个令人惊讶的行为：（i）2湿颗粒之间的倾斜碰撞最初形成一个旋转的团聚体，这可能会在稍后的时间分离，及（ii）3湿颗粒之间的正常碰撞在牛顿？的摇篮设置，当运行在一系列的影响速度，显示所有可能的几何结果，除了显示由传统的（干）牛顿？的摇篮。假设（i）是由于离心力的作用，（ii）是由于所有3个颗粒之间同时发生的、流体介导的相互作用（而干牛顿？的摇篮被建模为一系列的2体碰撞）。基于润滑、毛细力和固体力学的实验和基本理论的组合将用于开发小团聚体的粘附/分离和破碎标准。该理论只需要可测量的固体和液体性质（没有可调参数）。一个逐步的方法将遵循，其中2粒子的实验和理论是最初的重点，其次是两个扩展到3粒子系统。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。通过对湿谷物简单剪切流动的研究，将评估液体层对连续变量（如应力）的影响。此外，离散颗粒模拟也将进行两个特定的单元操作，即转鼓和流化床造粒（或扩大），在努力描述非直观的行为观察到颗粒和气固系统，分别。 这项工作将是PI（Robert Davis教授）和联合PI（克莉丝汀Hrenya教授）之间的合作，他们在与流体和颗粒流相关的理论、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理解，（ii）将新理论纳入MFIX框架，MFIX框架是一个免费的、开放源代码的多相系统建模，可供世界各地的研究人员使用，（iii）在颗粒技术领域培训学生，这已被确定为国家需求[1-3]，（iv）与技术团体（通过演示、同行评审的出版物和网站）、学生团体（通过纳入共同主要研究者开发的粒子技术课程和推广）和非科学团体分享所学到的信息，以及（v）积极鼓励代表性不足的少数群体。这项工作的一个独特的方面是使用一个？斯托克斯？摇篮？（类似于传统的牛顿？的摇篮，但与液体添加到碰撞球）作为一个实验装置;广泛熟悉这个桌面玩具将利用在示范K-12的学生和教师，以及非科学界。

CBET-0754825, DavisIntellectual Merit. Processes involving the flow of solid particles are ubiquitous in both nature (landslides, avalanches, 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 systems are found in a wide range of applications (fluidized-bed granulation, mixing of pharmaceuticals, pollen transport, filtration, etc.), and are known to display characteristics atypical of 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. Preliminary experiments display two surprising behaviors: (i) an oblique collision between 2 wetted particles initially forms a rotating agglomerate, which may separate at a later time, and (ii) a normal collision between 3 wetted particles in a Newton?s cradle setup, when run at a series of impact velocities, displays all possible geometric outcomes except that displayed by a traditional (dry) Newton?s cradle. It is hypothesized that (i) is due to the role of centrifugal forces and (ii) is due to the simultaneous, fluid-mediated interaction between all 3 particles (whereas the dry Newton?s cradle is modeled as a series of 2-body collisions). A combination of experiments and fundamental theory based on lubrication, capillary forces, and solid mechanics will be used to develop stick/separate and breakup criteria for small agglomerates. The theory will require only measurable solid and liquid properties (no adjustable parameters). A stepwise approach will be followed, where 2-particle experiments and theory are the initial focus, followed by an extension of both to 3-particle systems. 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 wet grains. Furthermore, discrete-particle simulations will also be carried out for two specific unit operations, namely rotating drums and fluidized-bed granulation (or enlargement), in an effort to describe non-intuitive behaviors observed in granular and gas-solid systems, respectively. This work will be a collaboration between the PI (Prof. Robert Davis) and the co-PI (Prof.Christine Hrenya), who have extensive background in the theoretical, experimental, and simulation aspects associated with fluid and particulate flows.Broader Impacts. The broader impacts of the work include the following: (i) a more fundamental understanding of wetted particulate systems, (ii) incorporation of the new theory into the MFIX framework, a no-cost, open-source code for modeling multiphase systems, available to researchers worldwide, (iii) training of students in the area of particle technology, which has been identified as a national need [1-3], (iv) sharing of learned information with the technical community (via presentions, peer-reviewed publications, and web sites), the student community (via incorporation into Particle Technology course developed by the co-PI and outreach), and the non-scientific community, and (v) active encouragement of underrepresented minorities. A unique aspect of this work is the use of a ?Stokes? cradle? (similar to the conventional Newton?s cradle, but with liquid added to the colliding balls) as an experimental apparatus; the widespread familiarity with this desktop toy will be capitalized upon in demonstrations to K-12 students and teachers, as well as the non-scientific community.