Investigation of a novel serpentine micromixer based on Dean flow and separation vortices

Passive micromixers, due to their relatively high mixing efficiency and simple fabrication, have wide applications in biological, medical, and chemical processes. Serpentine and convergent-divergent micromixers are typical kinds of these micromixers. In the present study, a combination of sinusoidal and serpentine microchannels with two types of sinusoidal walls is investigated numerically and experimentally for the Reynolds number ranging from 0.01 to 100. Three-dimensional steady-state Navier–Stokes equations coupling with convection–diffusion equation are solved on a structured mesh to determine the flow field and the species concentration distribution. The microchannel is fabricated using PDMS by employing soft lithography. The results show that by adding convergent-divergent regions, the mixing index can be improved by 99.89% at Re = 100. Maximum mixing efficiency is achievable by using serpentine-sinusoidal mixers with a smaller number of mixing units compared to the serpentine mixer. It is demonstrated that the centrifugal force, the formation of Dean vortices, and sudden contraction–expansion are the main reasons for the increment of mixing efficiency. Micromixers with a smaller amplitude and larger number of bumps present a larger coefficient of performance.