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978-3-8439-4524-0, Reihe Thermodynamik
Local Measurement of Gas-Liquid Mass Transfer with Chemical Reaction in Coiled Capillaries
155 Seiten, Dissertation Technische Universität Dortmund (2020), Softcover, A5
Gas-liquid reactions in microreactors play an important role in academic and industrial research. The increased surface-to-volume ratio in microreactors leads to enhanced heat and mass transfer and allows to overcome mass transfer limitations in gas-liquid reactions. Mass transfer can be further increased by employing helically coiled capillaries, which induce Dean vortices and improve radial mixing.
In this work, a colorimetric measurement method is proposed for gas-liquid slug flow in straight and helically coiled capillaries in order to visualize local mass transfer phenomena and concentration distributions. This method is based on the consecutive oxidation of leuco-indigo carmine and enables a non-invasive investigation of mass transfer and chemical selectivity in microchannels with high spatial resolution.
In a further step, an Arduino-based slider setup is developed, which is equipped with a computer-vision system to track gas-liquid slug flow. This setup is combined with the colorimetric method in order to increase the temporal resolution, which allows for the validation of numerical simulations and the investigation of the entire lifetime of a single liquid slug. Volumetric mass transfer coefficients are measured and compared with data from literature and the mass transfer contribution of the liquid film is discussed.
By utilizing the colorimetric method, it is further possible to visualize the superposition of Taylor and Dean vortices in coiled capillaries. Depending on the flow conditions five different flow regimes are identified with different intensities of Taylor and Dean vortices affecting the oxygen distribution within the liquid phase. Dimensionless numbers are derived that describe the transitions in flow regimes and the interplay between local hydrodynamics and chemical selectivity is evaluated.