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

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。0933242 Jaeger随着工业过程对颗粒尺寸的要求越来越小，更好地了解粉末的行为变得越来越重要。此外，越来越多的人认识到，即使在名义上较大的粉末中也存在细粉，这严重影响了它们的流动性。使致密的颗粒状粉末流动特别具有挑战性的是同时起作用的多种颗粒间作用力和涉及的尺寸范围，小到纳米级的颗粒表面粗糙度。在这一点上，自由落下的粉末流为研究颗粒颗粒以及颗粒与气体的相互作用提供了特殊的机会，因为它们使直接观察非常小的颗粒间力成为可能。自由落体流剖面的变化，特别是流分裂成粒子团的变化，可以作为微观、颗粒尺度相互作用的宏观特征和灵敏诊断。这项研究涉及一种独特的实验设备，旨在利用高速摄像机与颗粒物质一起坠落，跟踪两米自由落体过程中致密颗粒状粉末流的演变。将同动框架中的成像与广泛的计算机建模以及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，用来建立总体流动特性与它们对各种类型的粘性颗粒-颗粒相互作用的依赖之间的定量联系，包括毛细作用、范德华作用和静电力。广泛的影响：除了与适当控制颗粒物质相关的工业和经济价值外，颗粒材料的研究还提供了对跨越广泛的科学和工程学科的基本的、交叉的科学问题的见解。这项研究将培训研究生在颗粒物和多相流研究的关键方面，它包括一大群不同的本科生的积极参与，以及与工业合作伙伴的密切合作。这项研究将与一系列多方面的教育和外联活动相结合，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.