(224g) Mixing Enhancement in Three-Dimensional Helical Microchannels

We present experimental and numerical results on mixing performance for the flow of two miscible liquids in a three-dimensional helical microchannel. A novel yet straightforward method is developed to fabricate 3-D helical microchannels with different pitch length in a polydimethylsiloxane (PDMS) mold. This geometry provides a constant Dean number flow, due to the constant radius of curvature of the helix, which differentiate it from the existing planar spiral microchannels. The mixing performance is characterized, using digital image processing techniques, based on the mixing length which is defined as the stream-wise distance in the microchannel where the mixing has reached 90% of the full intensity. Experimental results show a minimum mixing length vs. Reynolds number as a common feature for all the microchannels of similar diameter and different pitch length. Increasing the Reynolds number beyond this minimum mixing length adversely influences the mixing performance by increasing the measured mixing length due possibly to the decrease in the residence time of the two streams in the microchannel. Numerical simulations are presented to support the experimental observations.