(435b) Effect of the Inlet Conditions On the Mixing Efficiency of a T-Shaped Micro-Mixer

We investigated the concentration patterns and the degree of mixing resulting from the confluence of two inlet fluid flows in a T-shaped micro-mixer. In particular, we focused on the symmetry breaking due to having a fully developed velocity profile instead of a flat one at the inlet.  It was found that when fully developed conditions are ensured, the engulfment occurs at relatively low Reynolds numbers, Re, with typical S-shaped symmetric contour plots. On the other hand, when the fluid flow at the confluence is non-fully developed and presents a plug flow region at the center, engulfment occurs at much larger Re and, in addition, we observe a C-shaped engulfment pattern (with the tracer crossing the mixing channel mid-plane either near the center or at the walls), with much lower mixing efficiencies.

In particular, for a specific mixing channel, that means that, as the inlet flow rate is increased, two engulfment points may be found, at different Reynolds numbers.  First, an S-shaped engulfment is observed at lower Re, when the inlet flows are fully developed; then, as Re is increased, the inlet channel length may not be long enough to ensure a fully developed flow conditions at the confluence, so that the engulfment disappears and the degree of mixing decreases. Finally, at an even higher Re, a C-shaped engulfment pattern is observed, corresponding  to the case of inlet plug flow. Moreover, it was observed that attention should be paid to the convergence criteria of the numerical simulations, as unstable solutions of the problem could be found even when residuals of all equations are well below 10^-7.