Multiscale Investigations of Reactive Bubble Flows

Bubble columns are widely used in chemical, petrochemical, biochemical and metal industry. Especially in reactive bubble columns, the efficiency is influenced by the local hydrodynamics. To increase the efficiency of any apparatus, the mutual interaction of the local hydrodynamics and chemical reactions must be considered, which is not covered by the state-of-the-start integral design methods. However, local description of hydrodynamics by CFD exists, but there are still some challenges to overcome when a coupling with local reaction conditions has to be established: 1. Influence of the bubble interaction onto the reaction 2. Influence of the bubble size on bubble behavior 3. Mutual interaction of reaction and hydrodynamics at high time and space resolution (bubble induced turbulence) As given in literature, individual phenomena were isolated investigated by experiments and numerical studies, but the interaction of these phenomena were mainly neglected. In this research project, a new multi-scale experimental and numerical approach is used. Initially the start is with well described test systems followed by the industrial relevant (organic) systems defined in the progress of the SPP. In a first step, experiments in a test cell (<500µl) will be performed with a high spatial and time resolution to investigate the effect of bubble interactions (bouncing, film drainage) on the mass transfer and reactions. Furthermore, experiments in a Venturi cell allow hydrodynamics and reaction investigations of an isolated monodisperse bubble swarm (<10 bubbles) being spatially captured by the counter-current flow. Finally, experiments in a 2D bubble column (polydisperse) will be performed, mimicking a real cylindrical bubble column. The influence of the hydrodynamics and the reactions will be measured taking into account the local bubble size by optical probes. The hydrodynamics and turbulence are resolved by laser based measurement techniques (PIV, LIF, PDA) and is the basis for code validation. For the reactive bubble interactions, a mesh free solver (FPM) is used, which is able to track the interface without reconstruction. Hence, it can resolve the reactions at any location close to the interface and will support the experimental description at hydrodynamic stress of single and swarm bubbles on the reaction close to the interface. The modeling of a large-scale apparatus is then based on the Euler-Euler model to keep the computational costs low. Based on the experimental results, a turbulence model will be selected and optimized. The implementation of the pH- and temperature dependent reactions allows a first description and detailed analysis of the reactive bubble column. The result of the project will lead to a better understanding of the mutual influence of hydrodynamics and reaction on different scales. The numerical investigations will therefore increase the accuracy of layout and reduce efforts for time and cost intensive pilot experiments.

 

Technische Universität Kaiserslautern
Fachbereich Maschinenbau und Verfahrenstechnik

 

Project leader
Dr.-Ing. Mark W. Hlawitschka