Electromagnetic tailoring of vortex patterns in an electrolyte layer at the millimeter scale

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The action of Lorentz forces in electroconductive fluids is able to enhance the transfer of heat and mass by promoting stirring in a controlled manner. This is particularly important at small scales where Lorentz forces have been used to accelerate electrochemical reactions or modify the morphology of electrodeposits. In this paper, we show that different laminar vortex patterns in a weak electrolyte layer can be tailored on a millimeter scale by electromagnetic stirring generated by the interaction of a dc current and different distributions of neodymium magnets of 1.5 mm diameter. We report particle image velocimetry measurements and neatly visualized images obtained by long exposure photography of steady electromagnetically driven flows that take place in a 10 mm × 10 mm region with a layer thickness of 1 mm. Owing to the weak strength of the Lorentz force and to the millimeter scale confinement of the shallow electrolyte layer, a Reynolds number of Re≈2 was reached. Under these conditions, flow quasi-two-dimensionality is achieved, which is quantitatively verified through a numerical model that is able to replicate the experimental results with a high degree of accuracy. Results show that Lorentz forces can be tailored on a millimeter scale to promote vortex flow patterns that can improve transport processes.