Mass transfer of rising gas bubbles in reacting liquids

• Applicant: Professor Dr.-Ing. Matthias Kraume
• Subject Area: Chemical and Thermal Process Engineering
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256647858

The idea of this project is the investigation of the influence of the interaction of bubbles on the mass transfer in reactive bubbly flows. Previously, the experimental work was focused on the determination of the interaction between fluid dynamics, mass transfer and chemical reaction. As in practical applications multiple bubbles interact, here certain bubbles in different types of bubble formations will be investigated. The experimental systems developed in the first funding period will further be used for complementary single bubble experiments. These experiments provide the necessary basic information to evaluate the results of interacting bubble formations.The aim of the complementary single bubble investigations is the determination of mass transfer coefficients. These are determined based on the change of the bubble size during the bubble's contact with the (reacting) liquid phase. The experiments are performed in two apparatuses which were further developed in the first funding period. The apparatuses are a bubble ascent channel and a counter current flow cell.Varied parameters are: The chemical system (WG Klüfers/Schindler/Herres-Pawlis), bubble size, contact time between bubble and liquid, pressure, temperature, educt concentration in the liquid phase.The results will be mathematically modeled with adjusted or new Sherwood correlations while reasonably incorporating all influencing parameters. These correlations will be used to compare systems with more complex velocity and concentration fields in the vicinity of the bubble. These fields will be created under controlled conditions. Several approaches will be tested. A chain of bubbles, an array of bubbles and a bubble swarm which will be stopped with a single bubble following will be investigated. For comparison, turbulence promoters which were developed and investigated in the first funding period by other groups in the priority program will be tested as well (WG Kähler/Schlüter/Thoeming). Besides the investigation of the chemical systems de-veloped in the first funding period, the new and further developed systems with parallel and/or consecutive chemical reactions will be investigated. In some cases, this requires new ap-proaches in the experiments to be able do an accurate quantification. The fully automated ex-perimental apparatuses will be equipped with new stationary and moving spectral measurement techniques (WG Rinke/Simon). This approach has great potential as chemical reactions are developed which have competing chemical reactions resulting in differing discolorations.The chosen approach of following the bubble during its ascent with an optical measurement technique provides results of the rising path, bubble shape and shrinkage behavior under diverse controlled conditions. This information is of high interest for numerically working groups as it can easily be used for validation (WG Bothe/Rzehak/Sommerfeld).

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