Mixing in Three Dimensional Linear Spiral Microchannels

Since its introduction a decade ago, soft lithography has drastically changed our understanding of fluid physics under confinement by enabling rapid production of microchannels and microdevices. Despite its popularity however, soft lithography has some limitations, including fabrication of thoroughly three dimensional passages without using multiple layers. In this talk, we first introduce the fabrication of a simple three dimensional linear spiral microchannel in a polydimethylsiloxane (PDMS) mold. In two dimensional planar spiral microchannels, Dean number increases or decreases with each consecutive rotation as the radius of curvature decreases or increases, respectively. In our three dimensional spiral microchannel, however, the radius of curvature is constant and as a result the Dean number assumes a constant value. The mixing performance of two miscible fluids in this microchannel is characterized using digital image processing techniques. The influence of flow rate as well as the length of the spiral pitch on the mixing performance is studied. Other possible applications are also discussed.