Mixing characterization in different helically coiled configurations by laser-induced fluorescence
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Mixing characterization in different helically coiled configurations by laser‑induced fluorescence P. Kováts1 · C. Velten1 · M. Mansour1,2 · D. Thévenin1 · K. Zähringer1 Received: 5 June 2020 / Revised: 30 July 2020 / Accepted: 14 August 2020 © The Author(s) 2020
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.
* K. Zähringer [email protected] 1
Lehrstuhl für Strömungsmechanik und Strömungstechnik, Otto-von-Guericke-Universität Magdeburg, 39106 Magdeburg, Germany
Mechanical Power Engineering Department, Faculty of Engineering, Mattaria, Helwan University, Cairo 11718, Egypt
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Experiments in Fluids
(2020) 61:203
Graphic abstract
Mass fractions of tracer fluid at Re = 500 in the six examined helix configurations. List of symbols A Cross-sectional area (m2) Af Area of a grid unit (m2) APixel Pixel area (m2) c Local concentration (kg/m3) − c Average concentration (kg/m3) CF Straight standard helix CFD Computational fluid dynamics CFI Coiled flow inverter CFR Coiled flow reverser d Tube diameter (m) D Coil diameter (m) 𝔇ab Mass diffusivity (m2/s) De Dean number (–) FEP Fluorinated ethylene propylene i Total coil number (–) I Intensity (counts)
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I Normalized intensities (–) I0 Minimum intensity (counts) IAVG Average Intensity (counts) Imax Maximum intensity (counts) L Total coil length (m) L1 Liquid 1 L2 Liquid 2 PLIF Planar laser-induced fluorescence Mc Mixing coefficient (–) n Refractive index (–) P Coil pitch (m) Q Volume flow rate (m3/s) Re Reynolds number (–) s Wall thickness (m) Sc Schmidt nu
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