Theoretical and experimental characterization of a low-Reynolds number split-and-recombine mixer

A mixing device based on the split-and-recombine (SAR) principle is characterized using both theoretical and experimental methods. The theoretical model relies on solving a ID diffusion equation in a frame of reference comoving with the flow, thus avoiding the usual numerical artefacts related to the prediction of high-Peclet number mixing. It accounts both for the hydrodynamic focusing of the flow inside the mixing channel and the nontrivial flow topology. The experimental technique used for quantifying the degree of mixing utilizes two initially transparent salt solutions that form a colored compound in a fast chemical reaction. The degree of mixing is derived from the average color saturation found at specific positions along the mixing channel. The data obtained from the theoretical model are in reasonable agreement with the experiments and underline the excellent performance of the SAR mixer, with a mixing length growing only logarithmically as a function of Peclet number.