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

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.