Segregation and Spatio-Temporal Dynamics of Granular Shear Flows

摘要- 0434279颗粒处理操作在各种各样的行业往往很难理解相比，他们的流体处理同行。产品质量和一致性经常受到诸如不均匀流动和组成成分分离等问题的威胁，后者在药品制造中尤其重要，其中保持均匀的颗粒混合物至关重要。传统上，启发式经验法则被用来限制这些问题，但这些并不能可靠地预测流动不稳定，也不能防止在放大或调试期间发生离析。从质量控制、商业或监管的角度来看，更可取的方法是能够从基本原理、材料特性和小规模实验室测试中定量预测流动不均匀性和分离率，然后设计相应的工艺，以限制对性能和产品均匀性的有害影响。虽然颗粒流的理论基础越来越多，但还没有广泛应用于工业中典型的非均匀或非定常流动。从根本上说，偏析源于系统相邻区域之间的速度和流动特性（如颗粒温度）的变化，这些变化会优先将某种类型的颗粒驱动到特定位置。因此，最初的目的是通过数值和实验表征库埃特流和泰勒-库埃特流中自发发生的流动不稳定性和相干结构。库埃特流和泰勒-库埃特流可能是最简单的几何模型，包括剪切和物理边界相互作用，这是实际流动的基本成分。粒子动态模拟技术将用于模拟粒子特性，并将使用傅立叶方法对所产生的流动进行表征，并与动力学理论的结果进行比较。实验流将使用x射线断层扫描，粒子图像测速（PIV），流采样和图像分析技术进行检查。随后将研究不稳定性作为偏析触发器的作用，最终计算给定粒子种的偏析通量。计算和物理实验将用于描述相关的无量纲群的混合-分离转变。潜在的不稳定性和自发的不均匀性将在原型2D和3D Couette和Taylor-Couette流动中进行研究，尽可能利用流体流动的类比。对于典型的混合或输送操作的高剪切流，将描述由不均匀性引发的颗粒偏析机制。将进行参数敏感性分析，以量化颗粒尺寸分布，密度变化，表面性质和颗粒长径比的作用。初期工作将考虑球形颗粒，后期工作将考虑非球形颗粒。在基本流动和偏析研究中很少考虑颗粒形状，但非球形颗粒在工业中占主导地位，并且已知对流动和偏析有强烈影响。特别地，针状的针状形态在药物晶体中很常见，这些将在实验中进行研究并在模拟中进行建模。本提案中的研究计划将与教育和推广计划相结合，包括研究生、本科生和高中粒子技术研究培训。粒子技术的培训被认为是一个国家需要的领域，但在美国一直被忽视。在美国生产的大部分产品都是颗粒形式或涉及重要的颗粒技术。事实上，有人认为，微粒的处理和制造至少与液体和气体的处理和制造同样重要。但在美国，大多数即将毕业的工程师在这一领域接受的教育很少。作为这项提议的一部分，PI将继续推动粒子技术进入罗格斯大学的课程。高中学生将有机会通过州长工程学院获得研究经验，该学院吸引新泽西州的高中生到罗格斯大学进行高中和大学的交流项目。最后，PI将继续以征聘妇女和少数民族为目标。

ABSTRACT - 0434279 Particulate processing operations in a wide variety of industries are often poorly understood compared to their fluid processing counterparts. Product quality and consistency is frequently threatened by problems such as non-uniform flow and segregation of constituent components, the latter being especially significant in pharmaceutical manufacture in which maintenance of a homogenous particle mixture is critical. Traditionally, heuristic rules-of-thumb have been used to limit these problems, but these have not reliably predicted flow instabilities and prevented segregation from occurring during scale-up or commissioning. A more desirable approach, from either a quality control, commercial, or regulatory perspective, is the ability to quantitatively predict flow inhomogeneities and segregation rates from fundamental principles, material properties and small-scale laboratory tests, and then to engineer processes accordingly to limit detrimental effects on performance and product uniformity. While there is a growing theoretical basis for granular flow, this has not yet been applied widely to non-uniform or unsteady flows which are typical of industrial situations. Fundamentally, segregation stems from variations in velocity and flow properties, such asgranular temperature, between adjacent regions of a system, preferentially driving particles of a certain type to particular locations. Thus, an initial aim is to numerically and experimentally characterize the flow instabilities and coherent structures occurring spontaneously during Couette and Taylor-Couette flows. Couette and Taylor-Couette flows are perhaps the simplest model geometries encompassing both shear and physical boundary interactions, essential ingredients of practical flows. Particle dynamic simulation techniques will be used to model particle properties and resulting flows will be characterized using Fourier methods and compared to results from kinetic theory. Experimental flows will be examined using Xray tomography, Particle Image Velocimetry (PIV), stream sampling, and image analysis techniques. The subsequent role of instabilities as triggers for segregation will then be investigated, culminating in calculations of segregation flux for a given particle species. Computational and physical experiments will be used to characterize mixing-segregation transitions in terms of relevant dimensionless groups. Underlying instabilities and spontaneous inhomogeneity will be examined in archetypal 2D and 3D Couette and Taylor-Couette flows, utilizing analogies with fluid flows where possible. Mechanisms of particle segregation triggered by the inhomogeneities will be characterized, for high-shear flows typical of mixing or transport operations. A parametric sensitivity analysis will be performed to quantify the role of particle size distribution, density variations, surface properties and particle aspect ratio. Initial work will consider spherical particles with work in latter years allowing for non-spherical particles. Particle shape is rarely considered in fundamental flow and segregation studies, but non-spherical particles predominate in industry and are known to strongly influence flow and segregation. In particular, acicular needle-like morphologies are common in pharmaceutical crystals and these will be studied experimentally and modeled in the simulations. The research initiatives in this proposal will be integrated with educational and outreach initiatives including graduate, undergraduate and high school research training in particle technology. Training in particle technology has been recognized as an area of national need but has traditionally been neglected in the US. A large proportion of the products manufactured within the US are in particulate form or involve significant particle technology. In fact, it has been argued that the handling and manufacture of particulates is at least as important as that of liquids and gases. But the majority of graduating engineers in the U.S. receive little education in this field. As part of this proposal, the PI will continue to advance particle technology into the curriculum at Rutgers. High school students will be given the opportunity for research experience through the Governor's School of Engineering, which attracts New Jersey high school students to Rutgers for a high school-university exchange program. Finally, the PI will continue to target the recruitment of women and minorities.