Freely-Falling Granular Powder Streams as Sensitive Probes of Interparticle Forces

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。0933242 Jaeger更好地了解粉末的行为变得越来越重要，因为工业过程需要越来越小的颗粒尺寸。此外，越来越多的人认识到，即使在名义上较大尺寸的粉末中，细粉的存在也会严重影响其流动性。使致密颗粒粉末流动特别具有挑战性的是同时起作用的大量颗粒间力以及所涉及的尺寸尺度范围，小至纳米级颗粒表面粗糙度。在这方面，自由下落的粉末流为研究颗粒-颗粒以及颗粒-气体相互作用提供了特殊的机会，因为它们可以直接观察非常小的颗粒间力。自由下落流剖面的变化，特别是流分解成颗粒簇，可以作为宏观特征和微观颗粒尺度相互作用的灵敏诊断。该研究涉及一个独特的实验设施，旨在跟踪超过两米自由落体的致密颗粒粉末流的演变，使用高速摄像机与颗粒材料一起下落。将同向移动坐标系中的成像与广泛的计算机建模以及通过原子力显微镜和扫描电子显微镜对颗粒表面的表征相结合，用于建立整体流特性与其对各种类型的内聚颗粒-颗粒相互作用（包括毛细管力、货车范德华力和静电力）的依赖性之间的定量联系。除了与颗粒物的适当控制相关的工业和经济价值外，颗粒材料的研究还提供了对广泛的科学和工程学科中基本的交叉科学问题的见解。该研究将培养研究生在颗粒物和多相流研究的关键方面，它包括一个庞大而多样化的本科生群体的积极参与，以及与工业合作伙伴的密切合作。这项研究将与多方面的教育和推广活动相结合，包括与附近的芝加哥科学与工业博物馆的活动。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0933242JaegerA better understanding of the behavior of powders is becoming increasingly important as industrial processes require smaller and smaller particle sizes. In addition, there is a growing realization that the existence of fines even in nominally larger sized powders critically affects their flowability. What makes dense granular powder flows particularly challenging is the multitude of interparticle forces that are at work simultaneously and the range of size scales involved, down to nanoscale particle surface roughness. In this regard, freely falling streams of powder offer special opportunities to investigate particle particle as well as particle-gas interactions because they make it possible to observe very small interparticle forces directly.Intellectual Merit. Changes in the free falling stream profile and, in particular, the break up of the stream into particle clusters can serve as macroscopic signatures and sensitive diagnostics of microscopic, grain-scale interactions. The research involves a unique experimental facility designed to track the evolution of dense granular powder streams over two meters of free fall, using a high speed video camera falling alongside the particulate material. The combination of imaging in the co-moving frame with extensive computer modeling and with characterization of grain surfaces by atomic force microscopy and scanning electron microscopy is used to establish a quantitative connection between the overall stream properties and their dependence on various types of cohesive particle-particle interactions, including capillary, van der Waals and electrostatic forces.Broader Impact: In addition to the industrial and economic value associated with the proper control of particulate matter, the study of granular materials provides insights into fundamental, crosscutting scientific issues across a wide range of science and engineering disciplines. The research will train graduate students in key aspects of particulate matter and multi phase flow research, and it includes the active participation of a large and diverse group of undergraduates as well as a close collaboration with an industrial partner. The research will be integrated with a multi faceted set of education and outreach activities, including activities with the nearby Chicago Museum of Science and Industry.