MICROFLUIDICS

Streams Swirled by Dean

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Science  02 Jun 2006:
Vol. 312, Issue 5778, pp. 1281
DOI: 10.1126/science.312.5778.1281a

In microfluidic systems, mixing of the low-volume fluid streams is hindered by slow diffusion rates and smooth flow behavior. Although mixing can be enhanced using external energy, passive approaches that rely on the channel geometries are often preferred for sensitive materials. However, such passive strategies can require complex, expensive channel fabrication, such as elaborate three-dimensional (3D) networks and incorporation of groove or ridge features in the channels.

Sudarsan and Ugaz present an easily fabricated passive design, composed of simple 2D smooth-walled channels. The mixing enhancement arises from Dean flow: the transverse flow field induced in curved channels by the interplay of centrifugal effects and inertial axial motion. A planar split-and-recombine arrangement generated alternating layers of different fluids. When two colored streams moved through the curve, counterrotating Dean vortices caused them to flow through one another and exchange position. In a second device, the authors incorporated an abrupt increase in the channel cross-sectional area, which induced expansion vortices that enhanced mixing in the horizontal dimension. At the same time, vertical mixing occurred through Dean flows brought on by an asymmetric serpentine geometry. — MSL

Proc. Natl. Acad. Sci. U.S.A. 103, 7228 (2006).

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