Collaborative Research: Grain and Gas Motion in Dense Granular Flows

国家科学基金会-化学运输系统分部颗粒多相过程计划（1415）提案编号：0651628主要研究者：Walsworth、罗恩所属机构： 哈佛大学提案标题：合作研究：在稠密颗粒流中的颗粒和气体运动核磁共振和磁共振成像（NMR/MRI）将用于非侵入性地研究两种稠密颗粒流系统中颗粒和气体的运动：气体流化床和垂直通道流。该项目将在两个关键方面超越以往对这些系统的核磁共振/磁共振研究：（a）将使用一种同步气泡生成技术，通过气体和谷物核磁共振探测流化床中气泡的时空结构;和（B）气体运动和交换将在流化床中探索，比以前可能的NMR研究大得多（直径达50厘米），作为对直接工程相关的床的研究的一步。作为一个合作项目，拟议中的工作将联合收割机结合NMR的专门知识，在颗粒流中的颗粒在马萨诸塞大学，阿默斯特，与专业知识的超极化气体NMR在沃尔斯沃思实验室在哈佛。这项合作将是至关重要的同步气泡实验，以确保粮食和气体的数据可以采取相同的颗粒流stations.Intellectual MeritPrevious工作在这个项目上已经使用粮食和超极化气体核磁共振探索速度场和气体-乳化液交换在气体流化床，但由于混乱的随机发生的气泡的能力，急剧测试模型已受到限制。在这个新项目中，气泡将与NMR采集同步产生，从而可以建立颗粒和气体运动的详细图像。目前的理论思想的玻璃，历史依赖性的致密颗粒流体的性质将直接面对，将模型的气体流动和交换机制。大型流化床的低场超极化气体核磁共振研究。常规NMR对大型系统的适用性受到在整个样品体积上需要强的均匀磁场的严重限制。相比之下，超极化气体NMR可以在低得多的磁场下工作，这对于工业规模的应用是实用的。作为将颗粒介质的NMR方法扩大到工业规模的一步，将在现有的低场MRI装置中建造一个大型流化床，并使用超极化技术研究气体的运动和交换。这项合作是独一无二的，因为它能够将超极化气体NMR应用于大型流化床的开创性研究。重力驱动的垂直通道（料斗或筒仓）流是一种基本的颗粒剪切流，但由于缺乏非侵入式探针，其三维结构的信息很少。核磁共振/磁共振成像将用于研究重力驱动的垂直槽道流的流场和时空相关结构。密集颗粒剪切流的本构关系将被测试和相关结构的增长和衰减，如力链将被探索作为流动参数changed.Broader ImpactsA参与研究的本科生（包括许多来自代表性不足的群体）的强大传统将继续，除了传统的研究生研究和培训。现有的跨学科，机构间的合作将得到加强，使新的核磁共振技术，如超极化气体对软物质物理问题的影响。这个大规模的低场核磁共振项目应该为非侵入性核磁共振技术的真正工业规模应用铺平道路。

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)Proposal Number: 0651628 Principal Investigators: Walsworth, Ron Affiliation: Harvard University Proposal Title: Collaborative Research: Grain and Gas Motion in Dense Granular Flows Nuclear magnetic resonance and magnetic resonance imaging (NMR/MRI) will be used to noninvasively study the motions of grains and gas in two dense granular flow systems: the gas fluidized bed and vertical channel flow. This project will extend beyond previous NMR/MRI studies of these systems in two key aspects: (a) a synchronous bubble-generation technique will be used to probe the space-time structure of bubbles in a fluidized bed, both with gas and grain NMR; and (b) gas motion and exchange will be explored in fluidized beds much larger than previously possible for NMR studies (up to 50 cm diameter), as a step towards studies of beds of direct engineering relevance. As a collaborative project, the proposed work will combine the expertise for NMR on grains in granular flows in the Candela lab at UMass, Amherst, with the expertise for hyperpolarized-gas NMR in the Walsworth lab at Harvard. This collaboration will be crucial for the synchronous-bubble experiments, to ensure that grain and gas data can be taken for identical granular flow states.Intellectual MeritPrevious work on this project has used grain and hyperpolarized-gas NMR to explore the velocity field and gas-emulsion exchange in gas-fluidized beds, but due to the chaotic random occurrence of bubbles the ability to sharply test models has been limited. In this new project bubbles will be created synchronously with NMR acquisition, permitting a detailed picture of grain and gas motion to be built up. Current theoretical ideas on the glassy, history-dependent nature of dense granular fluids will be directly confronted, as will models of the gas flow and exchange mechanisms. Large-scale fluidized bed studied by low-field hyperpolarized-gas NMR. The applicability of conventional NMR to large systems is severely constrained by the need for a strong, uniform magnetic field over the entire sample volume. Hyperpolarized-gas NMR by contrast can function with much lower magnetic fields, practical for industrial-scale applications. As a step towards scale-up of NMR methods for granular media to industrial scales, a large-scale fluidized bed will be constructed in the existing low-field MRI setup and use hyperpolarized techniques to study the motion and exchange of gas. This collaboration is unique in its ability to perform this groundbreaking research of applying hyperpolarized gas NMR to a large-scale fluidized bed. Gravity-driven vertical-channel (hopper or silo) flow is one of the basic granular shear flows, yet little information exists on its structure in 3D due to the lack of noninvasive probes. NMR/MRI will be used to study the flow field and space-time correlation structure of gravity-driven vertical-channel flows. Proposed constitutive laws for dense granular shear flows will be tested and the growth and decay of correlated structures like force chains will be explored as the flow parameters are changed.Broader ImpactsA strong tradition of involvement of undergraduates (including many from underrepresented groups) in research will be continued, alongside traditional graduate research and training. Existing cross-disciplinary, inter-institutional collaboration will be enhanced to bring novel NMR techniques such as hyperpolarized gas to bear on soft-matter physics problems. This large-scale low-field NMR project should pave the way for true industrial-scale applications of noninvasive NMR techniques.