Visualization and quantification of chaotic mixing for helical-type micromixers

The paper presents a micro mixer structures fabricated by an interesting technique of embedded twisted threads in polydimethylsiloxane (PDMS), which is polymerized and cured. After removing the threads carefully, the remaining channel structure is studied concerning the flows and mixing characteristics. Three-, four-, and six-strand-helical fluid microchannels (d _h ?=?100?μm, L?=?3?mm) with a specified helix angle (θ?=?22°) were used to conduct the experiments. The electroosmotic flow, inlet velocity, local velocity at specified positions, and sample concentration distribution along a downstream direction were measured via microparticle image velocimetry and laser-induced fluorescence techniques, respectively. Local mixing efficiency and mixing length were obtained at very low Reynolds numbers (≤0.0242) and low Peclet numbers (≤65.8). Results show that four-strand micromixer has the best mixing performance. Finally, a correlation of mixing length with Pe was developed, which might be applicable to a microbiomedical device design.