Wet Particle Collisions

在雪崩、泥石流和花粉捕获等自然现象中，会发生覆盖着薄液体层的固体颗粒的碰撞和流动。它们也普遍用于工业过程，如包衣药物粉末、肥料颗粒和巧克力糖果，用于这些产品的储存和控制释放。为了更好地理解这些现象，有必要预测粒子在碰撞后粘在一起或弹开的条件。类似地，重要的是要知道当受到力时，湿颗粒的稠密悬浮液何时将流动，以及何时将锁定或堵塞。该奖项将使用实验室实验和计算机模拟来阐明湿颗粒碰撞的基本物理学，并开发涉及湿颗粒的流动的预测模型。该奖项的目标是（1）开发两个或多个湿颗粒碰撞的新微物理模型，（2）利用新的实验方法来验证和改进模型，（3）将微物理模型结合到离散元方法中，以模拟许多湿的碰撞颗粒的流动;（4）培养为未来的研究人员和领导者做好充分准备的学生。建模方法将采用自然坐标系为每个相互作用的粒子对，分解成正常和切向运动，包括润滑，毛细，离心和固体接触力。它将确定微观物理的结果，如粘附和反弹，使宏观尺度的湿颗粒流现象，包括堵塞和团聚，可以预测。这些实验将使用空气台和高速摄像机来观察安装在螺旋桨式圆盘上的湿球的碰撞，从而避免了基于螺旋桨的实验中由弦带来的限制。该奖项的结果将使研究人员能够有效地模拟湿颗粒流，并提供对液体力在实质性改变这些致密颗粒系统行为中的作用的新理解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Collisions and flows of solid particles covered with thin liquid layers occur in natural phenomena such as avalanches, mud slides, and pollen capture. They are also prevalent in industrial processes such as coating pharmaceutical powders, fertilizer pellets, and chocolate candies for storage and controlled release of these products. To better understand these phenomena, it is necessary to predict the conditions under which the particles stick together or bounce apart after colliding. Similarly, it is important to know when a dense suspension of wet particles will flow when subject to forces and when it will instead lock or jam. This award will use laboratory experiments and computer simulations to elucidate the fundamental physics of collisions of wet particles and to develop predictive models of flows involving wet particles.The goals of this award are (1) to develop new microphysical models for collisions of two or more wet particles, (2) to utilize new experimental approaches to verify and refine the models, (3) to incorporate the microphysical models in a discrete element method for simulating the flows of many wet, colliding particles, and (4) to train students who are well prepared as future researchers and leaders. The modeling approach will employ a natural coordinate system for each interacting pair of particles, resolved into normal and tangential motions and including lubrication, capillary, centrifugal and solid-contact forces. It will determine microphysical outcomes such as sticking and bouncing, so that macroscale phenomena of wet granular flow, including jamming and agglomeration, may be predicted. The experiments will use an air table and high-speed camera to observe collisions of wetted spheres mounted on hockey-type pucks, thereby avoiding limitations imposed by strings in pendulum-based experiments. The outcome of this award will allow researchers to effectively model wet granular flows and provide new understanding of the role of liquid forces in substantially changing the behavior of these dense particulate systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.