Numerical Evaluation of Liquid Mixing in a Serpentine Square Convergent-divergent Passive Micromixer

Abstract

AbstractMicromixers are crucial components to carry out chemical, biomedical and bio-chemical analyses on µTAS (micro total analysis system) or Lab-on-chips. Simple planar type passive mixers are always most desirable over three dimensional or complex geometries of passive mixers or active mixers as they are less expensive, easy to fabricate, and easy to integrate into complex miniaturized systems. However, at very low Reynolds numbers (0 to 100), due to the inherent laminar nature of the microfluidic flows, mixing remains challenging in passive mixers. Previous studies reported that serpentine square-wave micromixer is one of the simple and effective passive device for micromixing. In the present study, to further enhance the mixing efficiency of the device, horizontal straight portions of serpentine square wave mixer are replaced with convergent-divergent passages and the mixing performance of both mixers are evaluated in the Re range of 0 to 100. It is observed in the low Re (0 to 10), mixing in the square wave mixer with convergent-divergent portions (SQW-CD mixer) is governed completely by pure diffusion as in the case of square wave mixer with straight horizontal portions (SQW mixer). However, at high Re (Re > 10), the presence of convergent-divergent portions in the SQW-CD mixer considerably intensify the stretching and folding of samples in the mixing channel. Additionally, the extra recess available at the bends of SQW-CD mixer creates recirculation zones in the mixer. Therefore, a significant improvement in the mixing performance is achieved at high Re (Re > 10) for SQW-CD mixer as compared to conventional SQW mixer. This would allow shorter mixing lengths for SQW-CD mixer as compared to Sq wave mixer. However, with increase in Re, the rise in pressure drop is considerably high for SQW-CD mixer as compared to SQW mixer.