- 12:30 PM

New Perspectives for Reactive Mixing In Multiphase Flows

Stefan Radl and Johannes G. Khinast. Institute for Process Engineering, Graz University of Technology, Inffeldgasse 21a, Graz, 8010, Austria

Fast chemical reactions in sparged stirred tanks are of great importance in the chemical industry. If multiple reaction steps occur within one apparatus, a detailed understanding of mixing is crucial to precisely control the reaction network. Clearly, a quantitatively correct model of the interaction between reactions, mass transfer and liquid phase mixing is necessary to attain this goal.

Although there has been significant experimental and theoretical work in this field, fundamental challenges still remain. For example, fully resolved 3D simulations of reacting bubble swarms with complex reactions are still extremely demanding with respect to computational resources. Hence, our previous work1-3 was based on 2D direct numerical simulations of bubbly flows and three-dimensional effects were ignored completely.

In this work it is our intension to critically prove our previous assumption by using both theoretical and numerical arguments. Therefore we use different simulation approaches that allows us to simulate bubbly flows including mixing and reactions on different scales in full 3D. Our work includes direct numerical simulation of bubble wake phenomena and large eddy simulations to study bubble plume effects. The results of these simulations enable us for the first time to characterize the impact of mixing on the reaction network in different regions of a bubble plume. Finally, we propose new perspectives on how to model the complex dynamics in bubble swarms when fast reactions are involved.

(1) Radl S, Tryggvason G, Khinast JG. Flow and Mass Transfer of Fully Resolved Bubbles in Non-Newtonian Fluids. AIChE Journal. 2007;53:1861-1878.

(2) Radl S, Khinast JG. Prediction of mass transfer coefficients in non-Newtonian fermentation media using first-principles methods. Biotechnology and Bioengineering. 2007;97:1329-1334.

(3) Radl S, Koynov A, Tryggvason G, Khinast JG. DNS-based Prediction of the Selectivity of Fast Multiphase Reactions: Hydrogenation of Nitroarenes. Chem Eng Sci. 2008; in press.