Chaotic mixing of fluids in a planar serpentine channel

We have achieved rapid chaotic mixing of two fluids flowing in a planar serpentine convergent–divergent mini-channel, and analyzed the transient three-dimensional flow field and distribution of concentration. The degree of irregularity of trajectories is increased through experiencing a repeated configuration of turning with an amplified pressure gradient in the designed channel. The results reveal that the pattern of the alternating convergent–divergent cross sections induces corner Dean cells with much increased Dean numbers; the stretching and folding of interfaces are effectively enhanced, resulting in superior chaotic mixing of fluids. Viewed on cross sections normal to the main stream, the complicated trajectories appear to halt, swing and twist as the fluids approach the Dean cells. Along the stream, the flow trajectories become increasingly irregular. The flow trajectories of Dean cells are symmetric with respect to the central cross section; on each side of the cross section, the flow trajectories are highly unstable, spatially and temporally, around the Dean cell. In our mixing channel the Dean cells in the mixing channel are arranged across the interfaces; the interfacial area between fluids is continuously distorted and enlarged in a spiral behavior, thus effectively promoting the fluid mixing.