(266a) Micromixing Using Planar Curved Channels

The inability to achieve passive mixing in planar microchannels continues to be a challenging problem in microfluidic technology. Recent work has shown that by patterning channel walls with grooved structures, transverse flows can be generated to chaotically mix fluids. Other techniques involve flow lamination, either in serial or parallel formats, where multiple interfaces between fluids are created to increase the overall interface area for diffusive mixing to take place. Although these techniques have made useful contributions, most of them induce additional complexities to device fabrication, as the final channel structure is three-dimensional and requires more than one lithography steps. In this work, we show that planar curved channels can be used to mix fluids at length scales comparable to mixers from literature. Since uniform symmetric curved channels, like a serpentine channel, cannot be used to mix fluids as the interface just undulates between the channel walls, we pattern the serpentine channels with expansions at specific locations to generate vortices to promote mixing. By selecting the location of these expansions to coincide with the position along the curved flow path where the inner fluid is pulled towards the outer wall, the transverse Dean flow is reinforced by the action of the expansion vortices to maximize the interfacial area between the two fluids. Further, we show that by simply splitting the main channel into multiple narrower curved channels and rejoining them further downstream, the transverse Dean flow in each narrow channel can be harnessed to create a serial lamination mixer in a planar format. Finally, we show hybrid designs incorporating asymmetrically slanted barriers at specific locations in the curved flow path that are capable of effective mixing over a greatly expanded Reynolds number range than has been previously demonstrated.