Project Details
Projekt
Euler-Euler-Modeling of reactive flow in bubble columns
Applicant
Dr. Roland Rzehak
Subject Area
Fluid Mechanics
Chemical and Thermal Process Engineering
Chemical and Thermal Process Engineering
Term
from 2014 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 256651902
In the present project closure models for chemical reaction as well as the associated mass transport will be included in the Euler-Euler description of bubbly flows. This approach allows to capture inhomogeneous distributions of bubble number density and bubble size as well as local differences in concentration and flow fields on the scale of the bubble column. In this way calculations up to the size of industrial equipment or components thereof become feasible. Transport processes and chemical reactions on the scale of individual bubbles have to be taken into account by closure models to achieve this. Concerning purely fluid dynamical processes, a set of closure models has been defined at HZDR which encompasses the exchange of momentum between the bubbles and the surrounding liquid, the bubble-induced turbulence as well as bubble-coalescence and -breakup. The complete model was validated by comparison to a number of experimental data sets, including also bubble column experiments, so that a powerful model for the prediction of the fluid dynamical behavior of bubble columns is available. On this basis, closure models for the transfer of matter from the gas bubbles into the liquid shall now be qualified in an analogous way. To this end, simulation results obtained for different model variants are compared to suitable experimental data. An important parameter in this respect is the time scale of the chemical reaction: fast reactions take place mostly in the boundary layer around the bubbles, slow reactions in contrast mostly in the interior of the liquid phase. In addition, the type of the reaction plays an important role. Sufficiently validated closure models taking into account these kind of effects are not available yet. Mass transfer and fluid dynamics are coupled together, because a consequence of the absorption is a decrease of bubble size, which in turn is substantial in determining the flow. From this coupling interesting and yet only little explored phenomena may result. If for example the bubble size falls below a certain value along the height of the bubble column, a transition from the heterogeneous to the homogeneous bubble column regime may occur. This is accompanied by a qualitative change of both the distribution of gas and the flow pattern. Investigation of this kind of interrelations extends the fundamental understanding of reactive bubbly flows. The frame of the SPP1740 offers excellent possibilities to reach these goals since models for the mass transfer taking place at bubbles without or with simultaneous chemical reaction can be extracted from the work of other groups in the SPP. In a similar vein, lab scale experimental investigations of partners in the SPP can be used to validate the models, while the other way round simulations may aid the planning of future experiments.
DFG Programme
Priority Programmes
