Crossflow and mixing in obstructed and width-constricted rotating radial microchannel

The crossflow and mixing in rotating radial microchannels with various obstruction and/or width-constriction geometries have been investigated to improve samples/reagents mixing using a centrifugal microfluidic platform. It is found that a channel with repeated cycles, or patterns, of obstruction followed by width-constriction (OWC) provides the best mixing result. Crossflow in the microchannel is highly intensified even at moderate rotation speed less than 100 rad/s, due to the OWC configuration with increased mixing from a combination of (a) local centrifugal acceleration a_b that arises from flow negotiating corners of the obstructions in the channel, and (b) Coriolis acceleration a_cor induced from throughflow in the rotating microchannel, which is highly amplified in the two narrower sub-channels partitioned by the center obstruction in the channel as well as the downstream channel with width constriction. Moreover, mixing is further enhanced with flow splitting at the stagnation point of an obstruction followed by flow recombination with jet-jet impingement mixing downstream of the obstruction and upstream of the width constriction. Numerical and experimental models have been developed and their results agree well with each other. As much as 95% uniformity in mixing can be achieved for a short 30-mm long radial microchannel with repeated OWC patterns at a moderate rotation speed of 73 rad/s with Ek = 0.049 and Ro = 15.4. The performance of the rotating OWC channel far exceeds that of the stationary OWC channel, the rotating unobstructed/obstructed microchannel, and the rotating width-constricted microchannel. Although the present study is focused on momentum and mass transfer in rotating OWC microchannels, the benefit can lend itself to heat and other transfer processes.