Einladung zum Vortrag im Kolloquium Systemdynamik und Prozesstechnik

Simulation of Reactive Flows:
Micromixing in Multiphase Systems with Fast Reactions

Prof. Dr. Johannes Khinast , Rutgers State University of New Jersey

    Zeit: Freitag · 12. 7. 2002 · 14:00 Uhr
    Ort: Hörsaal V 9. 41 · Pfaffenwaldring 9 · Campus Stuttgart-Vaihingen

Abstract

novel, highly efficient solver for Navier-Stokes, mass and heat balance equations was developed, which allows the numerical simulation of flows with a large number of reacting species. A main advantage of our algorithm is that the code is stable even for very stiff reaction networks.
Using this solver, micro-mixing effects in multiphase flows were studied. Our group showed that the selectivity and yield of fast gas-liquid reaction networks depends on the flow around single bubbles, that is, mainly on the dynamics of the wake. Depending on bubble size and shape, the bubble wake can be either closed (with or without recirculation) or open (vortex shedding). Spherical bubbles have only closed wakes without recirculation, while all other bubble types exhibit recirculation or vortex shedding depending on their shape and the Reynolds number. A model was developed, which accounts for the flow around the bubble, mass transfer, and reactions. As a test reaction the oxidation of cyclohexane was chosen, which is a highly complex free-radical reaction of industrially importance for the manufacture of Nylon-6 and Nylon6,6 and other synthetic materials. The main results of our work are that (1) the different residence times in the bubble wake and at the bubble roof can lead to the formation of different products, (2) recirculation in the bubble wake acts as a transport barrier for the liquid-phase reactants, and (3) vortex shedding causes qualitatively different mixing patterns than a closed wake, thus leading to a different product distribution in the case of mixing-sensitive reactions.