Interface study of the fluids in passive micromixers by altering the geometry of inlets

This paper investigated the improvement in the mixing process of a T-shape micromixer owing to the significance of the mixing process in the microfluidics system. The geometry of a micromixer inlets was numerically investigated in this study. To this end, six different geometries for the flow entrance were designed and their effects on the mixing phenomenon inside the microchannel were evaluated. The fluid flow was laminar and incompressible, and the Reynolds numbers ranged from 25 to 250. The flow governing equations, including continuity equations, Navier–Stokes, and mass transfer were discretized through the COMSOL Multiphysics commercial software. An index entitled "mixing cost" was defined with concern to the simultaneous effects of the mixing coefficient and pressure drop in a microchannel. The results revealed that the increase in the Reynolds number generally increased the mixing coefficient. However, the incidence of some specific conditions disturbed this general order. This issue was explored in detail and its reasons were reported in the paper. Results show that the dominant factors in the quality of mixing are location, magnitude, direction of rotation and the number of vortexes as well as the Reynolds number. Likewise, according to the results, the mixing intensity and mixing cost parameters should be simultaneously investigated. It is because an increase in the mixing coefficient does not generally and necessarily mean a decrease in the mixing cost. This issue was studied and evaluated in six conditions, and the results were reported. Compared to the condition number 1, condition number 3 enjoyed a 37% increase in the mixing intensity and a 9% decrease in the mixing cost in Re = 250.