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

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.