Fluid mixing in a swirl-inducing microchannel with square and T-shaped cross-sections

This study investigated micromixers formed by a T-junction and a mixing channel consisting of serial modules formed by appropriately arranging the subsections with right shifted T-shaped, left shifted T-shaped and square cross-sections. The T-shaped cross-sections are constructed by protrusions and indentations on the channel wall. The variation of shape and size of the channel cross-section may induce a strong swirl structure of flow to enhance fluid mixing. Four parameters (the lengths of the three aforementioned subsections and the sequence of modules) were selected to optimize the micromixer, and computational fluid dynamics (CFD) together with Taguchi method was applied to select the values of the parameters. Then, the micromixer was fabricated by a lithography process and the mixing of pure DI water and a solution of Rhodamine B in DI water in the micromixer was observed by using a confocal spectral microscope imaging system. The numerical and experimental results, compared to those of a straight channel with the same hydrodynamic diameter, show that the novel micromixer with the deliberately designed geometry with a hydrodynamic diameter equal to 120 μm enhances fluid mixing efficiently at relatively low Reynolds numbers (0.01–10), corresponding to the mean velocities from 0.000081 to 0.081 m/s. The effects of the four parameters on fluid mixing in the proposed micromixer are examined by CFD simulation.