Experimental and Computational Studies of Fluid-Particle Flow Systems

Fluid-particle flow systems, such as fluidized beds, exhibit a rich array of complex physical phenomena and are vital to the pharmaceuticals, oil, chemicals and food industries. While these systems have been used industrially for nearly a century in processes ranging from fluidized catalytic cracking to granulation, they are also important in new applications to solve 21^st Century problems, such as chemical looping combustion for efficient carbon capture and sequestration. Currently, the energy and economic efficiency of these systems, as well as the use of these systems in new processes, is limited by a lack of in-depth understanding of the complex physics occurring in these systems over a wide range of length scales, and the relationship between this physics and reaction kinetics. Recently, the application of new experimental techniques and computational models has started to shed new light on these fascinating and industrially important physical phenomena.

Over the course of my research career, I have combined computational and experimental techniques to provide understanding of the fundamental science of fluidized beds beyond that which could be achieved using any individual technique. During my PhD at the University of Cambridge, I created a 3-D cylindrical Euler-Lagrange model of fluid-particle flow systems to simulate fluidized beds in their most commonly used state. I compared simulation predictions with previously obtained experimental results in order to validate the model, shed light on the nature of certain experimental techniques and reveal the origin of pressure oscillations in fluidized beds. Additionally, I developed new experimental techniques in order to conduct the first ever measurements of gas velocity and velocity distribution in a fluidized bed of particles using magnetic resonance imaging (MRI). These measurements provide the first data and details showing the distributions in gas velocities in different states of fluidization: minimum, homogeneous, and bubbling fluidization. I compared these results with classical analytical theory for gas flow in fluidized beds, in order to provide insights on the validity of theories used every day by industrial practitioners. As a post-doctoral researcher at Princeton University, I am bridging my doctoral research by investigating how computational predictions of gas phase dynamics match my experimental results. I am also branching out into new areas of fluid-particle flow by developing computational models to investigate wet fluidized beds, in which a small amount of liquid forms bridges between particles, leading to agglomeration, as well as falling granular jets which exhibit phenomena indicative of an effective surface tension.

As a research faculty member, I plan to expand upon the foundation I have built in order to explore the critical interplay between physics and chemistry in fluid-particle flow systems over multiple length scales. My research program will involve developing and combining multi-scale modeling and multi-scale measurement efforts to provide insights on physical phenomena that occur on length scales varying from one particle diameter to a reactor tens of meters in diameter. This research path will also entail coupling the chemical reactions with the modeling and measurement techniques in a way such that the relationship between the physical and chemical phenomena can be better understood. Finally, my program will involve direct collaboration with researchers and industrial practitioners who build fluidized beds for applications such as combustion and catalysis, in order to aid in the design and measurement of their experiments. My ultimate aim is to enable the next generation of two-phase granular flow systems, which can offer real world solutions to global challenges ranging from clean energy production to food supply to safe and economic production of pharmaceuticals.

I also intend to use my unique educational background, coming from a double major in physics and chemical engineering as an undergraduate at MIT to a PhD student and Gates Scholar at the University of Cambridge to a post-doctoral researcher at Princeton University, to enhance chemical engineering education at a research university. From my experiences, I have seen a number of ways in which the on-campus undergraduate and graduate education experience in the U.S. can be further enhanced. Firstly, as a supervisor in the education system unique to Oxford and Cambridge, I have seen the benefits of students discussing material and problems in 2-to-4-person student groups with a graduate-level supervisor in an organized yet open-ended discussion setting. Secondly, as a Gates Scholar, I have had the privilege of interacting with leading graduate students in diverse disciplines, ranging from international relations to public health to engineering; this experience has shown the exceptional and expansive nature of the graduate education that comes from discussing important research problems that cut across academic disciplines. As a faculty member, I plan to take an active role in education to ensure more chemical engineering students at my university are provided with these valuable learning opportunities.