Mixing sensitivity to the inclination of the lateral walls in a T-mixer

One of the simplest geometries for micro-mixers has a T-shape, i.e., the two inlets join perpendicularly the mixing channel. The cross-sections of the channels are usually square/rectangular, as straight walls facilitate experimental and modeling analysis. On the contrary, this work investigates through Computational Fluid Dynamics the effect of a cross-section with lateral walls inclined of an angle alpha as such an inclination may stem from different microfabrication techniques. Considering water as operating fluid, the same mixing performance as square/rectangular cross-sections is obtained for inclinations alpha <= 3 degrees; this indicates the maximum admissible error on the perpendicularity of the walls in the manufacturing process. Above this value, the presence of inclined walls delays the onset of the engulfment regime at higher Reynolds numbers, and for alpha > 23 degrees the mixing is hampered dramatically, as the flow is unable to break the mirror symmetry and enter in the engulfment regime. At low Reynolds numbers, the mixing is moderately improved for alpha > 10 degrees, because the vortex regime presents a lower degree of symmetry than that of T-mixers with straight walls.