CAREER: Magnetic Resonance Imaging of Periodically Structured Bubbling Phenomena in Dense Suspensions and Fluidized Granular Materials

气泡在含有固体颗粒的流体中上升的流动在自然界和工业中无处不在。例子包括从活火山熔岩中升起的气泡到为生物反应器提供空气的气泡。这些气泡的动力学对整体流动行为和反应器性能至关重要，但由于流体的复杂性质，这些系统的动力学很难预测。具体来说，(1)这些流体的不透明性质阻碍了气泡动力学的三维成像，(2)气泡的混沌运动阻碍了工业设备的模型开发和优化。CAREER奖旨在推进磁共振成像（MRI）技术，以研究复杂流体中的气泡动力学，其方式类似于MRI通过对人体内部进行成像而彻底改变医学的方式。该项目将利用振动和控制气流来构建气泡动力学，这样它们就会周期性地重复动力学，从而推进表征和建模，并最终优化工业设备的性能。除了对工业有益之外，该项目还将利用气泡流的视觉魅力来激励下一代科学家，特别是来自历史上代表性不足群体的学生，研究STEM领域。研究小组将通过面对面的推广和视频制作项目，让学生们参与到这些视觉上有趣的流程和他们的基础科学中来。该CAREER奖将支持协调实验和建模，以促进对颗粒材料和致密悬浮液中气泡流动的理解，并开发控制这些流动的机制。光学成像和MRI将与流动动力学和MRI协议的计算建模相协调，以协同发展表征能力，同时确定结构气泡动力学的方法。气泡流动的周期性重复性质将允许使用不同MRI技术获得的图像进行直接比较。将二维系统中的光学图像与三维系统中的MRI图像进行比较，将揭示复杂的流变学如何控制3D多相系统中的流动行为，以及导致3D中不同气泡结构的机制。将2D和3D模拟与实验直接比较，将测试流变学和整体计算流模型捕捉导致气泡结构的流固过渡的能力。对振动和气体流动条件的控制将创造控制气泡结构的设计规则。总的来说，研究者预计这种结合的方法将为复杂的流动和MRI提供重要的基础见解，同时也提供表征和流动操作途径，以优化现有的实践和产生新的技术。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。

Flows in which bubbles rise through fluids that contain solid particles are ubiquitous in nature and industry. Examples range from bubbles rising through lava in active volcanos to bubbles feeding air to bioreactors. The dynamics of these bubbles are critical to the overall flow behavior and reactor performance, but the dynamics of these systems are difficult to predict owing to the complex properties of the fluids. Specifically, (1) the opaque nature of these fluids prevents imaging of bubble dynamics in 3D, and (2) the chaotic motion of bubbles prevents model development and optimization of industrial equipment. The CAREER award seeks to advance magnetic resonance imaging (MRI) techniques to study bubble dynamics inside complex fluids in ways similar to how MRI has revolutionized medicine by imaging the interior of the human body. The project will utilize vibration and controlled gas flow to structure the bubble dynamics, such that they follow periodically repeating dynamics, to advance characterization and modeling, and, ultimately, to optimize industrial device performance. In addition to benefits for industry, this project will use the visually fascinating nature of bubbly flows to inspire the next generation of scientists, especially students from historically underrepresented groups, to study STEM fields. The research team will engage students with these visually interesting flows and their underlying science through both in-person outreach and a video production program.This CAREER award will support coordinated experiments and modeling to advance understanding of bubbly flows in granular materials and dense suspensions and develop mechanisms to control these flows. Optical imaging and MRI will be coordinated with computational modeling of both the flow dynamics and MRI protocols to synergistically develop characterization capabilities while identifying ways to structure bubble dynamics. The periodically repeating nature of the bubbly flows will allow direct comparison of images obtained using different MRI techniques. Comparison of optical images in 2D systems and MRI in 3D systems will reveal how complex rheology governs flow behavior in 3D multiphase systems and mechanisms that can lead to different bubble structuring in 3D. Direct comparison of 2D and 3D simulations with experiments will test the ability of rheological and overall computational flow models to capture fluid-solid transitions which lead to bubble structuring. Manipulation of vibration and gas flow conditions will create design rules for controlling bubble structures. Overall, the investigator anticipates that this combined approach will provide important fundamental insights into complex flows and MRI while also providing characterization and flow manipulation pathways to optimize existing practice and generate new technologies.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.