Experimental characterization of gas-liquid transport processes in a reacting bubble column using a neutralization reaction

• Applicant: Dr.-Ing. Katharina Zähringer
• Subject Area: Fluid Mechanics ; Chemical and Thermal Process Engineering
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256661637

The transport of CO2 from the gas phase (bubbles) into a slightly basic watery phase is used to investigate in a quantitative manner mass transfer in a bubble column, first considering the limit case of a fast neutralization reaction. This simple system is appropriate to optimize the complex experimental process. Additionally, it is possible in this manner to deliver early during the first phase of this project experimental data that can be used for validation and comparison by numerical partners within the SPP. The evolution of the pH is followed in space and time in the experiment using indicators (e.g., Uranin) and Laser-Induced Fluorescence (LIF). Thanks to a calibration and knowing the gas conditions at inflow and outflow, it is possible to measure in this manner mass transfer. In order to avoid shadows, light refraction and reflection due to the bubbles, a second, pH-independent tracer is used, allowing to correct the experimental images (2-Color-LIF). The measurement procedure is used first for isolated bubbles and bubble trains, then for small groups of bubbles, varying flow rates and typical bubble diameters. After optimizing the measurement tech-niques, a typical bubble swarm is finally considered. Using high-speed cameras it is possible to track in time bubble diameters, bubble pathlines and mass transfer. Particle Tracking Velocimetry (PTV) is used to measure bubble velocities and trajectories, based on the available experience in our group. Velocities of the liquid phase are measured by Particle Imaging Velocimetry (PIV). Using a stereo-PIV system, all three velocity components of the water phase can be acquired. It is possible in this manner to quantify the impact of hydrodynamics on mass transfer, delivering comparison data for numerical projects within the SPP. Since liquid properties play a considerable role concerning mass transfer, liquid viscosity and surface tension will be varied using different glycerine/water mixtures of known properties. Here again, mass transfer and hydrodynamics will be measured simultaneously.All experimental data will be made available as soon as possible to all project partners and to the entire research community through a database accessible on the Web. All people interested by comparisons and validations of numerical simulations can freely use those experimental results.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1740: The Influence of Local Transport Processes on Chemical Reactions in Bubble Flows
• Participating Person: Professor Dr. Dominique Thévenin