Design and test of a passive planar labyrinth micromixer for rapid fluid mixing

In this paper, we explore the possibility of improving the efficiency of Dean vortex-based mixers by only employing smooth-walled simple two-dimensional (2D) geometries. Numerical simulation results reveal that the symmetries of Dean flows in the prevalent “S-shaped” mixers can be broken up by adding a simple 180° turn between two consecutive curved channels. A planar labyrinth micromixer that is composed of multiple such mixing units is designed for improved mixing. The mixer is fabricated in a single lithography step and the labyrinth has a footprint of 7.32 mm × 7.32 mm. Experiments using fluorescein isothiocyanate solutions and deionized water demonstrate that our design achieves fast and uniform mixing within 9.8 s to 32 ms for Reynolds numbers (Re) between 2.5 and 30. For the first time, multiple fluid bands are observed at Re = 5 in a simple 2D microchannel design without using obstructions or split-and-recombine features. An inverse relationship between mixing length and mass transfer Péclet number (Pe) is observed. Due to the simple planar structure, the micromixer can be easily integrated into lab-on-a-chip devices where passive mixing is needed.