Honors and Awards

• Elsevier Lifetime Achievement Award, AIChE Particle Technology Forum, 2022
• Distinguished Professor, Indian Institute of Technology, Madras, 2019
• Graduate Mentoring Award, Princeton University, 2016
• Permanent Guest professor, TU Hamburg-Harburg, 2014
• Humboldt Research Award, 2014
• Engineering Council's Excellence in Teaching Award, Princeton University, 2005, 2008, 2012
• JM Burgers Visiting Professor of Fluid Mechanics, TU Delft, 2009-2012
• Associate Editor, AIChE Journal, 2002-2011
• Neal R. Amundson Lecture, University of Houston, January 2010
• JM Burgers Lecture, Eindhoven, The Netherlands, 2009
• Fellow, American Institute of Chemical Engineers, 2008
• Moore Distinguished Scholar, California Institute of Technology, 2007
• The President's Award for Distinguished Teaching, Princeton University, 2006
• Thomas Baron Award in Fluid-Particle Systems, American Institute of Chemical Engineers, 2005
• School of Engineering & Applied Science Distinguished Teacher Award, Princeton University, 2005
• Distinguished Alumnus Award, Indian Institute of Technology, Madras, 2000
• Richard H. Wilhelm Award, American Institute of Chemical Engineers, 1999

Affiliations

• Associated Faculty, Andlinger Center for Energy and the Environment
• Associated Faculty, Princeton Environmental Institute
• Associated Faculty, Princeton Materials Institute
• Associated Faculty, Program in Applied and Computational Mathematics

Research Interests

Mechanics of multi-phase flows: Dispersed multiphase flows, frequently encountered in large reactors and separation devices, often manifest complex structures at different length and time scales – micro, meso, and macro scales – which influence the mixing, mass and heat transfer, and reaction processes. In the case of gas-particle flows, inter-particle forces due to van der Waals and electrostatic interactions and liquid bridges that form when the particles are wet further complicate the flow behavior in large process units. Inter-particle forces affect the flow behavior in small hand-held devices such as dry powder inhalers as well. Our research seeks to understand various aspects of these complex flows and develop simplified models. Some examples include:

• Develop coarse (filtered) models for transport and reaction by averaging over the micro- and meso-scale structures, so that they can be used to probe macro-scale coherent structures in these flows. In particular, we formulate coarse constitutive relations for interphase interaction force and effective stresses and test the predictions of the coarse models against experimental data on gas-particle flows in fluidized beds and risers.
• Develop models for the interplay between contact (triboelectric) charging of particles and flow. In particular, we quantify charging through experiments, formulate models for charging and charge transport, and examine the coupling between flow and charging in vibrated and fluidized beds and dry powder inhalation.
• Examine through large-scale simulations how inter-particle attraction (van der Waals or liquid bridge force) alters the gas-particle flow characteristics and develop coarse models for particle phase rheology that capture these effects.

In these studies, we use several different computational approaches to probe the underlying physics:

• (~10³ particles) Particle-resolved flow simulations where the Lattice Boltzmann Method is used to simulate the fluid motion and Newton’s equations of motion coupled with soft sphere collision models (Discrete Element Method, DEM) are solved to track the motion of the particles,
• (~10⁶ particles) Eulerian-Lagrangian (often referred to as CFD-DEM) simulations where the locally averaged equations of motion for the gas are coupled with DEM simulations of particles, which are supplemented with additional equations for the electric field, liquid distribution in the case of wet particles, etc.,
• (~10⁶ parcels) Eulerian-Lagrangian (often referred to as CFD-DPM) simulations where the locally averaged equations of motion for the gas are coupled with DEM simulations of parcels consisting of many particles, and
• Eulerian-Eulerian two-fluid model simulations

Heterogeneous catalytic reactions enabled by plasma and light (jointly with Professor Bruce Koel): Non-thermal plasma and photons are known to enhance the rates of heterogeneously catalyzed chemical reactions and change the optimum catalyst, allowing in some cases the reactions to be catalyzed by earth-abundant materials. We are interested in two pathways to rate enhancement:

• Vibrational and electronic excitation of gas phase reactants that enhances the rates of their dissociative adsorption on catalytic surfaces (possible with both plasmas and light), and
• Reactivity enhancement by excitation of the plasmonic resonance of metal nanoparticles dispersed on high-surface area support (possible with light).

Our research group is studying related reaction engineering issues, such as:  

• How deep into the catalyst particles can plasma penetrate and have a beneficial effect? How does the nanosecond pulsing of plasma affect the catalyst effectiveness factor? To address these questions, we study the kinetics of ammonia synthesis in a dielectric barrier discharge plasma reactor loaded with supported catalysts having different structures and distributions of active catalytic materials.