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Quantifying macro-mixing and micro-mixing in a static mixer using two-tracer laser-induced fluorescence

Abstract

An experimental procedure has been developed to quantify mixing at large scales (flow-induced) and at small scales (induced by molecular diffusion). It relies on the simultaneous imaging of two different fluorescent tracers using planar laser-induced fluorescence (PLIF). In order to quantify micro-mixing, a suitable neutralization reaction involving the fluorescent tracer uranine has been identified. Using PLIF, uranine is measured simultaneously with another fluorescent tracer, pyridine 2, employed to characterize macro-mixing. Since both tracers are quite inexpensive, this procedure allows an in-depth characterization of mixing properties even in large installations, by measuring the concentration fields of the involved tracers in a non-intrusive manner. This measurement procedure has been applied to a static mixer segment with geometrical features and dimensions similar to that found in practical applications. Laminar inflow conditions are employed. The flow and mixing analysis obtained by post-processing the measurement results is detailed in the present article.

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Acknowledgments

The authors would like to acknowledge the financial support of the German Research Foundation (DFG) through the Priority Programme “Analyse, Modellbildung und Berechnungen von Strömungsmischern mit und ohne chemische Reaktion” (SPP1141). The identification of a suitable chemical system has taken almost 2 years of intensive work. The active support of S. Leschka, S. Busse, M. Cordes, K. Kohse-Höinghaus, and S. Schwedler during our first attempts to find a suitable reacting system is gratefully acknowledged. Complementary flow simulations are realized in the research group of G. Wittum by V. Aizinger.

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Correspondence to Andreas Lehwald.

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Lehwald, A., Thévenin, D. & Zähringer, K. Quantifying macro-mixing and micro-mixing in a static mixer using two-tracer laser-induced fluorescence. Exp Fluids 48, 823–836 (2010). https://doi.org/10.1007/s00348-009-0769-4

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Keywords

  • Test Section
  • Static Mixer
  • Concentration Field
  • Fluorescent Tracer
  • Uranine