Magnetic Resonance Imaging and Modeling of Gas and Particle Flow in Fluidized Beds

颗粒状(即沙状)颗粒的集合通常表现得像固体一样；然而，通过这些颗粒向上流动的空气可以使它们表现得像起泡的液体，正如在工业过程装置中所观察到的那样，这种情况被称为“流态化床”。流态化床用于能源、制药和食品行业，以及用于碳捕获和封存的新兴行业。磁共振成像(MRI)用于非侵入性地观察人体内部的结构和运动，但它也可以用于成像其他3D不透明系统中的动力学。该项目将使用核磁共振技术来研究流态化床中气泡周围的气体和沙状颗粒的运动，并将利用这一知识来提高对系统的科学理解。反过来，这种理解可以量身定做，以支持环境技术。除了创造科学和技术洞察力之外，该项目还将使从高中到博士水平的学生的教育受益。来自邻近哈莱姆区和布朗克斯区的高中生将在研究生的监督下进行实验室研究，提供亲身体验，揭示类似液体的粒子流动及其广泛应用的惊人物理。高中生将制作泡状流的视频，以提高他们对科学的理解，同时教育同学和普通公众泡状流的迷人本质。流态化是指通过向上的气流将颗粒悬浮起来，从类固体状态转变为类流体状态的过程。气体的空隙或“气泡”通过流态化的颗粒上升，导致颗粒混合等正面效应，以及气固接触减弱等负面效应。因此，了解气泡周围气体和颗粒的详细流动物理对于优化一些技术以及开发新的可定制工艺至关重要。这些气泡与传统液体中的气泡有很大不同，因为气泡和颗粒相之间没有表面张力，气体在气泡和颗粒之间的周围空隙之间自由传递。由于无法“看到”3D不透明系统内的动态，这些气泡周围流动的科学知识主要是理论上的，大量的假设是在分析和计算模型中做出的。如果没有对气泡周围气体和颗粒动力学的可靠测量，各种假设的准确性在很大程度上还没有得到评估。最近，该项目的研究小组证明了磁共振成像可以用来测量鼓泡床中的气体和颗粒动力学。尽管核磁共振的时间分辨率很低，但该团队已经证明，通过同步核磁共振测量和可重复注入的气泡，可以有效地在3D中成像单个气泡周围的瞬时动力学。在这里，PI打算描绘气泡周围的气体和颗粒动力学，同时改变临界流动条件，以深入了解这些条件如何影响动力学。定量测量将用于评估分析和计算模型的有效性和需要改进的领域。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Collections of granular (i.e. sand-like) particles normally behave like a solid; however, flowing air up through these particles can make them behave like a bubbling liquid, as observed in industrial process units called “fluidized beds”. Fluidized beds are used in the energy, pharmaceuticals and food industries and in emerging industries for carbon capture and sequestration. Magnetic resonance imaging (MRI) is used to see structure and motion within the human body non-invasively, but it can also be used to image dynamics inside other 3D opaque systems. This project will use MRI to study the motion of both the gas and the sand-like particles surrounding bubbles in fluidized beds and will use this knowledge to improve scientific understanding of the systems. In turn, this understanding can be tailored to enable environmental technologies. Beyond creating scientific and technological insights, this project will benefit the education of students from the high school to the PhD level. High school students from neighboring Harlem and Bronx communities will conduct laboratory research under the supervision of graduate students to provide hands-on experience in uncovering the amazing physics of liquid-like flow of particles and its widespread applications. The high school students will create videos of the bubbly flows to improve their understanding of the science while educating classmates and the general public on the fascinating nature of bubbly flows.Fluidization is the process of suspending granular particles by upward gas flow, transitioning from a solid-like state to a fluid-like state. Voids or “bubbles” of gas rise through fluidized particles, inducing positive effects such as particle mixing as well as negative effects such as diminished gas-solid contact. Thus, understanding the detailed flow physics of gas and particles around bubbles is critical to optimizing a number of technologies as well as developing new tailorable processes. These bubbles are much different from those in conventional liquids, since there is no surface tension separating the bubble and particulate phases and gas passes freely between the bubbles and the surrounding interstices between particles. The inability to “see” the dynamics within 3D opaque systems has left the scientific knowledge of flow around these bubbles largely theoretical, with significant assumptions made in analytical and computational models. Without robust measurements of gas and particle dynamics surrounding bubbles, the accuracy of various assumptions has gone largely unassessed. Recently, the research team for this project has demonstrated that MRI can be used to measure gas and particle dynamics in bubbling fluidized beds. Despite the low temporal resolution of MRI, the team has shown that by synchronizing MRI measurements and reproducibly injected bubbles, effectively instantaneous dynamics around a single bubble can be imaged in 3D. Here, the PI intends to image the gas and particle dynamics surrounding bubbles while varying critical flow conditions to generate insights on how these conditions affect dynamics. The quantitative measurements will be used to assess the validity and areas for improvement in analytical and computational models.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.