Experimental study of Newtonian fluid mixing in T-shaped micromixers with variable obstacles across flow ratios

Mixing fluids at a microscopic scale is challenging due to flow stability, which makes mixing in microchannels a microfluidic challenge. Diffusion is slow, but passive mixing using sharp changes in flow direction and obstacles can induce convective and advective mixing that is still necessary to understand. In this study, seven T-shaped micromixers with symmetrical inlet channels and cylindrical, rectangular parallelepiped, or triangle prism obstacles in the outlet channel were fabricated using polydimethylsiloxane via soft lithography. The micromixers were tested in the laboratory, where flows were visualized under a microscope and captured using a high-frequency monochromatic camera. After digital processing of the images, the flows were characterized for Reynolds numbers Re ∈ [40, 200] and input flow ratios of 1, 2, 3, and 4. The physical phenomena influencing flow and mixing quality were analyzed to identify which factors promote effective mixing. The effects of two processes namely flow asymmetry in geometrically symmetrical inlet channels and the placement of obstacles in the outlet channel were also evaluated. It was found that, under symmetrical inlet conditions, introducing multiple obstacles in the outlet channel enhances mixing. However, for Re > 119, the mixture quality for asymmetric inlet flows decreases with the presence of obstacles in the outlet channel.