(382a) Direct Numerical Simulation of Reactive Deformable Bubble Swarms in Non-Newtonian Fluids

In many industrial applications, where reactants are initially available in different phases (i.e., gas and liquid), sparging bubbles is the scheme of choice for bringing these phases in contact. An additional, secondary role, often played by the gas bubbles is that of providing local continuous-phase mixing. In many chemical engineering applications (polymers and polymer solutions, animal cell cultures, fermentation processes, wastewater treatment, etc.) the liquid phase cannot be treated as a simple Newtonian fluid. Because of the special features of non-Newtonian fluids (shear thinning effects, viscoelasticity) up to now only a few numerical simulation studies, mostly based on lattice Boltzmann methods, were able to treat all aspects of non-Newtonian bubble flows correctly. The even more challenging analysis of mass transfer and chemical reactions in these rheological complex fluids is limited to experimental data.

In our work, we performed Direct Numerical Simulations of reactive bubble swarms with continuously evolving dynamic interfaces in non-Newtonian fluids, which is an extension of our previous works on Newtonian fluids [1, 2, 3]. A reactive species conservation model has been used in the simulation and therefore, the grid spacing of the computational domain has to be refined drastically in comparison to the fluid dynamics calculations only. Due to these restrictions and the limited available computer technology, the simulations are based on 2D flows with low to medium Reynolds-Numbers. The applied rheological models range from simple generalized Newtonian fluid models to the more complex viscoelastic models. The obtained flow field enables us to study the mass transfer and chemical reactions taking place in multiphase flows of single bubbles and bubble swarms in a quantitatively correct way. Furthermore, we can compute mass transfer coefficients of deformable bubbles and bubble swarms in non-Newtonian fluids, replacing lengthy measurements. In addition we can use the method to predict the yield and selectivity of chemical reactions taking place in a bubbly flow.

1 A. Koynov, G. Tryggvason, M. Schlüter, J.G. Khinast, 2006, Controlling Mass Transfer and Reactions in Reactive Bubble Swarms, Applied Physics Letters (accepted)

2 A. Koynov, J.G. Khinast, 2005, Micromixing in Bubble Swarms, Chemical Engineering and Technology 77

3 A. Koynov, G. Tryggvason, J.G. Khinast, 2005, Mass Transfer and Chemical Reactions in Bubble Swarms with Dynamic Interfaces, AIChE J. 51