PAssive Mixing in Microfluidic Spiral and Asymmetric Serpentine Channels

Keywords:
microfluidics, mixing, curved channels, dean flows

Abstract:
Mixing fluids at the microscale poses a variety of challenges, many of which arise from the fact that diffusion is the only available mechanism to achieve mixing in laminar flows. We present the use of microfluidic devices incorporating spiral curved channel geometries capable of achieving high levels of mixing, while retaining a planar format that can be fabricated using only a single or two lithography steps. Mixing is achieved in these spiral channels by making use of secondary flows characterized by the Dean number (_). Higher levels of mixing can also be achieved by breaking the symmetry in the value of _ between segments of flow path possessing opposing curvature. We demonstrate this using a serpentine geometry in which the width of the flow channel varies from one bend to the next. Although conventional serpentine geometries are ineffective mixers in the laminar flow regime, the variation in channel width associated with our design alters the value of _ thereby altering the transverse component of the flow trajectory as the fluid is advected downstream. The ensuing repeated winding and unwinding of the interface between the parallel streams is accompanied by a rapid expansion of the interfacial area available for diffusive transport.

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Nanotech 2005 Conference Program Abstract