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；然而，流动的空气穿过这些颗粒会使它们表现得像冒泡的液体，就像在工业过程中被称为“流化床”的装置中观察到的那样。流化床在能源、制药和食品工业以及新兴工业中用于碳捕获和封存。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，但它也可用于其他3D不透明系统内部的动态成像。该项目将使用核磁共振成像来研究流化床中气泡周围的气体和砂状颗粒的运动，并将利用这些知识来提高对系统的科学理解。反过来，这种理解可以调整以实现环境技术。除了创造科学和技术见解，这个项目将有利于学生从高中到博士水平的教育。来自邻近的哈莱姆和布朗克斯社区的高中生将在研究生的指导下进行实验室研究，为揭示液体状粒子流动的惊人物理学及其广泛应用提供实践经验。高中生将制作气泡流的视频，以提高他们对科学的理解，同时向同学和公众宣传气泡流的迷人本质。流态化是由向上的气体流动使颗粒颗粒悬浮，从固体状态过渡到流体状态的过程。气体的空洞或“气泡”通过流化颗粒上升，产生积极的影响，如颗粒混合，以及消极的影响，如减少气固接触。因此，了解气泡周围气体和颗粒的详细流动物理特性对于优化许多技术以及开发新的定制工艺至关重要。这些气泡与传统液体中的气泡有很大不同，因为没有表面张力将气泡和颗粒相分开，气体可以在气泡和周围颗粒之间的间隙中自由通过。由于无法“看到”3D不透明系统内的动态，关于这些气泡周围流动的科学知识在很大程度上是理论性的，在分析和计算模型中做出了重要的假设。由于没有对气泡周围的气体和粒子动力学进行可靠的测量，各种假设的准确性基本上没有得到评估。最近，这个项目的研究小组已经证明，MRI可以用来测量鼓泡流化床中的气体和颗粒动力学。尽管MRI的时间分辨率较低，但该团队已经证明，通过同步MRI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态。在这里，PI打算在不同的临界流动条件下对气泡周围的气体和颗粒动力学进行成像，以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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.