Passive Micromixers with Interlocking Semi-Circle and Omega-Shaped Modules: Experiments and Simulations

This study presents experiments and computational simulations of single-layer passive micromixer designs. The proposed designs consist of chains of interlocking semicircles and omega-shaped mixing modules. The performance of the new designs is compared with the concentric spiral channel configuration. The micromixers are intended to be integrated into a lab on chip (LOC) micro-system that operates under continuous flow conditions. The purpose behind the multi-curvature in these designs is the introduction of Dean vortices in addition to molecular diffusion in order to enhance the mixing performance. The micromixers were fabricated in PDMS (Polydimethylsiloxane) and bonded to a glass substrate. A three-dimensional computational model of micromixers was carried out using Fluent ANSYS. In experiments, the mixing of a 1 g/L fluorescein isothiocyanate diluted in distilled water was observed and photographed using a charge-coupled device (CCD) microscopic camera. The obtained images were processed to determine the mixing intensity at different Reynolds numbers. The standard deviation (sigma) of the fluorescence indicates the mixing completeness, which was calculated along the width of the channel at various locations downstream from the channel inlet. The value of sigma = 0.5 indicates unmixed streams and 0 is for complete mixing. It is found that the two new designs have a standard deviation of nearly 0.05. Additionally, complete mixing was observed at the channel outlet as demonstrated by the fluorescence images and the numerical results. However, the location of complete mixing at different positions depends on the Reynolds number, which varies between 0.01 and 50. Good agreement was found between the experiment and the numerical results. A correlation to predict the length scale where complete mixing can be achieved is given in terms of the radius of curvature, the mixing module, and the Reynolds number.