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

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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.