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

CBET-0754825，戴维斯智力成绩。涉及固体颗粒流动的过程在自然界（山体滑坡、雪崩、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的颗粒的系统？即，湿固体。这样的系统在广泛的应用（流化床造粒，混合药物，花粉运输，过滤等）中被发现，并且已知显示其干燥对应物的非典型特征，即颗粒团聚体的存在。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。初步实验显示了两个令人惊讶的行为：(i)两个湿颗粒之间的斜碰撞最初形成旋转团块，稍后可能会分离；（ii） 3个湿颗粒在牛顿？当以一系列的冲击速度运行时，除了传统的（干燥的）牛顿？年代的摇篮。假设：(i)是由于离心力的作用，（ii）是由于所有3个粒子之间同时发生的流体介导的相互作用(而干燥的牛顿？S摇篮被建模为一系列的两体碰撞)。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/分离和破裂准则。该理论只需要可测量的固体和液体性质（没有可调参数）。我们将采取循序渐进的方法，首先以两粒子实验和理论为重点，然后将两者扩展到三粒子系统。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湿颗粒的简单剪切流动的检查来评估。此外，还将对两个特定的单元操作进行离散颗粒模拟，即旋转鼓和流化床造粒（或扩大），以分别描述在颗粒和气固系统中观察到的非直观行为。这项工作将由PI （Robert Davis教授）和副PI （christine Hrenya教授）合作完成，他们在流体和颗粒流动的理论、实验和模拟方面有着广泛的背景。更广泛的影响。这项工作的更广泛影响包括：(i)对湿颗粒系统有更基本的了解，（ii）将新理论纳入MFIX框架，这是一个免费的多相系统建模开源代码，供全世界的研究人员使用，（iii）在颗粒技术领域培训学生，这已被确定为国家需要[1-3]，（iv）与技术社区分享所学信息（通过演讲，同行评审的出版物和网站），学生群体（通过将其纳入由联合pi开发的粒子技术课程和外展活动）和非科学界，以及(v)积极鼓励未被充分代表的少数群体。这项工作的一个独特之处在于使用了？斯托克斯吗?摇篮吗?(和传统的牛顿相似？S摇篮，但在碰撞球中加入液体)作为实验装置；人们对这个桌面玩具的广泛熟悉，将在K-12学生和教师以及非科学界的演示中得到充分利用。

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.