Katharina Zähringer

Experimental Investigation of a Static Mixer for Validation of Numerical Simulations

The mixing behavior around a SMX-type static mixer segment has been investigated experimentally by using Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) simultaneously. The newly conceived experimental rig allows quantifying mixing, by measuring velocity fields and concentration fields for different Reynolds numbers along vertical and horizontal sections directly behind the mixer. A spectral analysis of the simultaneous PIV and PLIF measurements has been carried out, in order to determine the characteristic frequencies induced by the mixer and relationships between velocity and concentration. Furthermore, the mixing efficiency has been quantified by considering the segregation index. In order to quantify micro-mixing a chemical reaction, involving a fluorescent tracer, has been chosen and imaged simultaneously with the macro-mixing, characterized by another tracer. Theoretical micro-mixing models have been tested by considering their accuracy in reproducing experimental data and first comparisons between experimental and numerical velocity fields are presented. The experimental data is documented in a data base, freely accessible through Internet, to allow a quantitative validation of numerical codes.

Particle-image-velocimetry measurements in organic liquid multiphase systems for an optimal reactor design and operation

Hydrodynamic features are very important to find an optimal reactor design for the hydroformylation of long-chain alkenes. For this purpose, and for the validation of theoretical reactor concepts, velocity measurements in a model reactor system are necessary. Due to the difficult reaction conditions found in reality (toxic thermomorphic organic solvent system, high pressure, high temperature, limited fields of view in typically used model reactors) such measurements are not an easy task. In this work, comparative particle-image-velocimetry (PIV) measurements have been used to find out if (1) the substitution of the solvent with water, and (2) reducing operation pressure still lead to similar results. For this purpose, PIV measurements have been performed in a stirred tank reactor under reaction conditions (organic solvents, high pressure, high temperature), but also with water at reduced pressure levels. It is found that pressure (as expected) and also the employed solvents do not have a significant influence on the observed flow structures, although density and viscosity are rather different. Therefore, further systematic experiments are now carried out in a model reactor, completely built out of glass, with water filling, and at atmospheric pressure. A complete hydrodynamic characterization is thus possible, opening the door for optimization of the resulting hydrodynamic field and for detailed comparisons with theoretical reactor design as well as numerical predictions.Graphical abstract