The effect of varying radius of curvature on mixing in elliptical spiral microchannels

Effective mixing is essential for a wide range of microfluidics applications. Passive micromixers have attracted much attention during recent years due to their low-cost and simple fabrication procedures with less power input in their implementation to high-throughput microfluidics platforms. Increasing the efficiency of micromixers is possible with an optimum geometry of inertial microfluidic channels, which utilize Dean vortices and Dean flows for the enhancement of mixing. Recently, micromixers with curved microchannels have been introduced to the literature. Yet, the enormous potential of elliptical spiral microchannels has not been adequately revealed. This study aims to assess the mixing performance of five-loop spiral polydimethylsiloxane micromixers with spiral structures and elliptic structures, which have different initial aspect ratios with varying radii of curvature along the channel. The performances of these micromixers were evaluated by comparing the mixing indices and intensity profiles obtained from inverted fluorescence microscopy images over a broad range of Reynolds numbers between 10 and 100. Elliptical spiral microchannels were able to provide mixing indices up to 98% at a Reynolds number of 20. Overall, the utilization of ellipse-shaped microchannels appear to provide a passive control over the mixing performance at several locations through the microchannel