We show the emergence of reaction hot spots induced by three-dimensional (3D) vortices with a simple A+B→C reaction. We conduct microfluidics experiments to visualize the spatial map of the reaction rate with a chemiluminescence reaction and cross validate the results with direct numerical simulations. 3D vortices form at spiral-saddle-type stagnation points, and the 3D vortex flow topology is essential for initiating reaction hot spots. The effect of vortices on mixing and reaction becomes more vigorous for rough-walled channels, and our findings are valid over wide ranges of channel dimensions and Damköhler numbers.
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We sincerely appreciate Dr. Etienne Bresciani for the helpful discussions on flow topology. The authors thank the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for computational resources and also acknowledge support from NSF via Grant No. EAR1813526. P. K. K. acknowledges the College of Science and Engineering at the University of Minnesota and the George and Orpha Gibson Endowment.