Detailed analysis of reactive multiphase flows is still challenging due to the complex linked transport processes. Until now, there is no reliable and reproducible experimental method for gas‐liquid flows, which enables the local measurement of dissolved species concentrations of educts, products, and side products at well‐defined and reproducible hydrodynamic conditions. A vertically arranged glass channel is used to capture gas bubbles with well‐defined wake structures. The hydrodynamic conditions in the wake can be predicted by dimensionless numbers and adapted for most industrially relevant systems. An experimental apparatus is presented for the investigation of the interdependency between hydrodynamics, mass transfer, and chemical reaction. The applicability of the setup is demonstrated with a chemical test system that shows a strong color shift from colorless to blue when the gas‐liquid reaction takes place.
In this article, we present experimental and numerical techniques to investigate the transfer, transport, and reaction of a chemical species in the vicinity of rising bubbles. In the experiment, single oxygen bubbles of diameter d b = 0.55 . . . 0.85 mm are released into a measurement cell filled with tap water. The oxygen dissolves and reacts with sulfite to sulfate. Laser-induced fluorescence is used to visualize the oxygen concentration in the bubble wake from which the global mass transfer coefficient can be calculated. The ruthenium-based fluorescent dye seems to be surface active, such that the rise velocity is reduced by up to 50 % compared to the experiment without fluorescent dye and a recirculation zone forms in the bubble wake. To access the local mass transfer at the interface, we perform complementary numerical simulations. Since the fluorescence tracer is essential for the experimental method, the effect of surface contamination is also considered in the simulation. We employ several improvements in the experimental and numerical procedures which allow for a quantitative comparison (locally and globally). Rise velocity and mass transfer coefficient agree within a few percents between experiment, simulation and literature results. Because the fluorescence tracer is frequently used in mass transfer experiments, we discuss its potential surface activity.
The hydrodynamics of bubbly flows is dominated by bubble-induced turbulence and bubble-bubble interactions. Both phenomena influence the gas-liquid mass transfer as well as the mixing of reactants. If the time scales of mass transfer and mixing are in the same order as the time scales of a parallel-consecutive reaction, the yield and selectivity will be affected by the local hydrodynamics. An experimental setup is presented that enables the investigation of mass transfer during well-defined and adjustable bubble collisions. The influence of CO 2 bubble collisions on mass transfer is measured and modeled with a modified Sherwood number correlation. Further visualization of the concentration field in the vicinity of O 2 bubbles by means of laser-induced fluorescence demonstrates the dependency of mass transfer from a chemical reaction and permits the development of a first model approach.
This paper presents an investigation on the achievable gain in ultra wideband (UWB) indoor propagation channels through the application of diversity and multiple input multiple output (MIMO) techniques. Both, signal to noise ratio and channel capacity are investigated based on simulation results from a ray-optical simulator. In particular the different behavior of classic diversity approaches and spatial multiplexing MIMO is regarded.
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