Abstract
We successfully develop a novel PDMS-based microfluidics mixer, which incorporates an overlapping crisscross entrance with patterned microchannels, and acts as a high-performance micromixer. Such an entrance design generates significant tumbling and brings about axial advection between mixing fluids. The systematic numerical analysis and experimental investigation have been performed to identify the characteristics of the device. The microfludics-based mixer is recently becoming a prevalent study for widely application in genetic sequencing, environmental monitoring and drug delivery. Among those researches, passive mixing plays one of the major roles due to its low cost and easy fabrication. Microsacle mixing of two aqueous solutions is usually done by advection and diffusion. Generating flow fluctuation significantly enhances flow folding and stretching and results in the improvement of mixing process. For fluids in the Stokes flow field, however, the inertia of flow diminishes and the effective mixing by modulating advection turns into the main challenge of designing new micromixer. In addition, reducing the characteristic length of diffusion or increasing residence time of the fluids evolves the molecular diffusion inside the microchannels. With all these concerns, the present work presents a microfludics configuration comprising two patterned microchannels with one crossing on top of the other. Two chaotic mixing mechanisms are also comprised: (1) twisting and reorienting of the split streams through the first overlapping crisscross junction and (2) merging and re-stretching by the hyperbolic flow at next junction. Both the results of flow visualization and numerical simulation reveal that such a design stimulates significant three-dimensional crossflow at the intersection of two channels and also induces strong helical flow motion in the following mixing channels. The vertical tumbling behavior redistributes the downstream flow pattern to enlarge the interfacial area and to promote axial advection between two mixing fluids. The transversal momentum generated by the device contributes to agitate the streams to mix well. The pressure distribution and mixing performance also become superior as compared with that of T-type grooved micromixer. Numerical analysis shows that although the molecular diffusion is detracted at a greater Reynolds number due to less residence time, the enhancement of the advances between mixing fluids is more overwhelming. This novel design is thus applicable for a much wider range of Reynolds number. The variation of the ratio of two initial flow rates controls the mass transfer rates in the two channels and is possibly extensible to be a satisfactory active micromixer.