Mixing characterization in different helically coiled configurations by laser-induced fluorescence

Abstract

Flow Mixing of two miscible liquids has been characterized experimentally in three different helically coiled reactor configurations of two different lengths in the laminar flow regime at Re = 50…1000. A straight helical coil, a coiled flow inverter, and a new coiled flow reverser have been built, each in a 3-turn and a 6-turn configuration. Laser-induced fluorescence of resorufin has been used to visualize and quantify mixing in cross-sections throughout the reactors. A mixing coefficient is derived from the fluorescence images to allow for a quantitative measure and comparison of the six configurations. It becomes obvious from these experimental results, that an early flow redirection in the helical configuration is beneficial to mixing. The 3-turn reactors achieve nearly the same mixing coefficients as the 6-turn reactors with the double length. This can be explained by the stabilizing effect of the Dean vortices in the helix, which develop during the first two turns. After that, the liquid is trapped inside the vortices and further mixing is inhibited. Accordingly, the coiled flow inverter and coiled flow reverser configurations lead to much higher mixing coefficients than the straight helical coil. The results of these measurements are now used for validation of numerical simulations, which reproduce the geometrical and flow conditions of the experiments. Some exemplary results of these calculations are also shown in this article. Graphic abstract Mass fractions of tracer fluid at Re = 500 in the six examined helix configurations.

Experimental characterization of mixing and flow field in the liquid plugs of gas–liquid flow in a helically coiled reactor

“…Thus, ideal mixing is characterized by a solution with half the dye concentration of the initial one. The influence of the dye on the physical properties of the solution can be neglected, as has been shown by previous measurements (Kováts et al 2020).…”

“…The coil curvature ratio results in = d∕D = 0.111 . The manufacturing process of the helix reactor was established before by Kováts et al 2020. The FEP tube had been wound around a PVC kernel and placed into a transparent acrylic glass box (Fig.…”

“…1, right), filled with a liquid with the same refractive index as the FEP-tubes. The refractive index of the FEP-tubes has been studied in previous experiments (Kováts et al 2020) and corresponds to n = 1.3405. Therefore, a mixture of glycerol and de-ionized water with a glycerol concentration of 5.25 vol% was used and controlled with a refractometer (Abbemat 200 from Anton Paar, accuracy ± 0.000100 nD).…”

A colorimetric technique to characterize mass transfer during liquid-liquid slug flow in circular capillaries

“…Note : Aqueous solution of glycerol is a good alternative to the continuous phase used here, the exact concentration of glycerol could be determined by refractometer and observation over optical distortion of employed capillaries, refer to [25] for details. Lift the immersion pool up, letting the inlet 3 and outlet 2 face upward.…”

Challenges in transfer of gas-liquid reactions from batch to continuous operation: dimensional analysis and simulations for aerobic oxidation

“…Nevertheless, flow reactors offer the opportunity to apply spectroscopic methods providing spatial concentration profiles, which is improving the knowledge gain during process development [17,18]. Furthermore, the understanding of fluid dynamics and mixing inside the milli and micro channels is improved, recently [19,20]. This progress together with the combination of computational fluid dynamics (CFD) and spectroscopic methods allows to analyze the mass transfer characteristics and thus minimize the uncertainties in prediction [21,22].…”