Spatially resolved experimental analysis and modeling of mass transfer from rising gas bubbles under influence of swarm turbulence with superimposed chemical reaction

• Applicant: Professor Dr.-Ing. Jorg Thöming
• Subject Area: Chemical and Thermal Process Engineering ; Fluid Mechanics
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256704298

The mass transfer from a dispersed gas phase into the liquid phase is of high importance in chemical industry and biotechnology, especially when a chemical reaction is superimposed. However, for a design of gas-liquid reactors, only empirical correlations are available, which show limited transferability. This is because they are based on integrally measured data obtained under specific conditions. For a more general description of the mass transfer performance for reactive systems and under swarm turbulence conditions via balance equations, three-dimensional velocity fields as well as concentration fields are required. In the first project phase swarm turbulences, induced by particle grids, were validated for certain gas flows. Based on this, the method of measuring, evaluating, and reconstructing three-dimensional concentration fields of bubble wakes were developed further by the laser induced fluorescence (LIF). This now allows measurements under hydrodynamic swarm conditions. The analysis of the three-dimensional concentration wake showed in case of a zigzagging gas bubble a Sherwood number of Sh = 470, which lies perfectly within the expectations. This shows that the developed optical method is very well suitable for validating numerical mass transfer calculations. When including Particle Image Velocimetry (PIV), however, even more precise velocity fields can be expected.In the project phase to come, the influence of superimposed reactions on mass transfer within bubble wakes is to be investigated as well as conversely the influence of mass transfer, interacting with reactions, on their selectivity. Under swarm turbulences, PIV/LIF measurements of mass transfer data for the SPP reaction system Fe-NO are scheduled as well as Nuclear Magnetic Resonance (NMR) measurements for flow conditions of reduced complexity (Taylor flow). For this purpose we will adapt the SPP's lead experiment Taylor flow on NMR requirements for measuring SPP reaction systems Fe-NO and Cu-O2.Furthermore we want to describe analogies and differences of mass transfer phenomena in wakes of single bubbles in laminar Taylor flow as well as under turbulent swarm conditions. Together with chemically, experimentally, and numerically working groups of the SPP, this analysis is intended to lead into the identification of a phenomenological modelling of mass transfer in gas-liquid reactors.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1740: The Influence of Local Transport Processes on Chemical Reactions in Bubble Flows
• Co-Investigator: Privatdozent Dr. Wolfgang Dreher