Ben Glasser, Rutgers University
"Scale-up of Particle Flow and Heat Transfer for Pharmaceutical Operations"
Granular materials are encountered throughout nature and across almost all industries, ranging from mineral processing to pharmaceutical manufacturing. Unit operations handling granular materials are notoriously inefficient and plagued by problems rarely encountered in their fluid counterparts. In this work we consider flow and heat transfer in an agitated bed of particles to better understand agitated drying of pharmaceutical materials. The complexity of the pharmaceutical drying process stems from the fact that heat transfer, mass transfer, and changes in physicochemical properties can occur simultaneously throughout drying. Complications often plague the procedure, including issues such as lengthy drying times, over-drying, nonuniform drying, agglomeration, attrition, and form changes. These circumstances make agitated drying a complicated process to understand and control. When considering scale up, these challenges are coupled with the difficulties typically associated with transferring knowledge from lab scale to pilot or manufacturing scale. As a result, it can be difficult to design an appropriate drying protocol that optimizes heat transfer and minimizes attrition from scale to scale. In our work, we have decoupled the problem and focused on studying flow and heat transfer for agitated drying. In this talk, we present results on the influence of process and material parameters on heat transfer in an agitated bed of particles. Our approach consists of employing a combination of experiments and particle dynamic simulations to analyze how mixing and heat transfer scale with bed parameters. For heat transfer we have carried out a design of experiments and computed heating times as well as heat transfer coefficients for the different conditions. We have also examined temperature distributions to characterize how parameters affect the uniformity of the bed. We find that scaling influences the flow and compressibility of the bed and therefore creates a balance between conduction and granular convection as the dominant mode of heat transfer. Using dimensionless analysis, we are able to collapse all the results into two heating regimes: 1) a regime where the bed heats slowly at a nearly uniform temperature, and 2) a regime where the system heats as a solid body with temperature decreasing with distance from the wall. Based on the different heating regimes, we are able to derive equations that predict the particles’ average temperature and temperature distribution. We discuss how these results can be used to inform drying protocols and scale-up strategies for bladed mixers and dryers.
Benjamin Glasser received his BS (1989) and MS (1991) in Chemical Engineering from University of the Witwatersrand, Johannesburg, South Africa. He obtained his PhD, also in Chemical Engineering, from Princeton University (1996), USA. He then spent a year as a postdoctoral fellow at Cambridge Hydrodynamics Inc. In 1997 he joined the Department of Chemical and Biochemical Engineering at Rutgers University where he is currently a Professor. His honors include the Merck Excellence Faculty Development Award, the Bristol-Myers Squibb Young Faculty Award, the Rutgers University Scholar-Teacher Award for excellence in research and teaching, Rutgers Outstanding Engineering Faculty Award, the PSRI Award in Fluidization and Fluid Particle Systems from the AIChE, and election as a Fellow of the AIChE. Professor Glasser serves as Director of the Pharmaceutical Engineering Program and Director of the Catalyst Manufacturing Consortium at Rutgers. His research interests include flow and segregation of granular materials, drying of particulates, the mechanics of fluidized beds, multiphase flows and reactors, and nonlinear dynamics of transport processes.