Flow regimes in T-shaped micro-mixers

Abstract

The different flow regimes occurring in T-mixers are investigated by means of direct numerical simulations. Three different values of the aspect ratio of the inlet channels, ki, that is their width to height ratio, are considered, namely ki= 0.75, 1 and 2. For the configurations with ki= 0.75 and 1, the same behavior as previously described in the literature, is found. In particular, as the Reynolds number is increased, the flow evolves from vortical to engulfment steady regimes, then to unsteady asymmetric and symmetric periodic regimes, until, finally, it becomes chaotic. All the critical values of the Reynolds number, at which the transitions between the different regimes occur, are found to be very similar for ki= 0.75 and 1, while some differences are highlighted in the vorticity dynamics and characteristic frequencies of the unsteady regimes. The observed scenario is completely different for ki= 2. Indeed, in this case, the flow evolves directly from the vortical regime to an unsteady symmetric behavior, with a vorticity dynamics that is significantly different from those observed for the other aspect ratios

Numerical investigation of flow regimes in T‐shaped micromixers: Benchmark between finite volume and spectral element methods

“…There is a very good agreement between the iso‐surfaces predicted with the two codes. Such vortical structures are those typical of the engulfment regime that, for the T‐mixer aspect ratio investigated here, occurs when . The engulfment regime is characterized by a tilting in the plane of the recirculation bubbles generated at the confluence of the streams at the top of the T‐mixer .…”

“…At such Reynolds number, the flow exhibits an unsteady time‐periodic behaviour with a Strouhal number , where is the characteristic time of the periodic motion. The vortical structures are typical of the unsteady asymmetric regime that occurs for .…”

“…The inlet channels have a square cross‐section, with mm, while the mixing channel presents a aspect ratio, i.e., mm, so that its hydraulic diameter is . The length of the inlet channels, mm , is enough to ensure a fully‐developed flow at the confluence, while the mixing channel length, mm , allows the complete evolution of vortical structures …”

Numerical analysis of lamination effect in a vortex micro T-mixer with non-aligned inputs

“…The results demonstrates that the new design of T-mixer provides a significant enhancement of mixing and presents lower pressure loss and similar level of shear stress compared to a typical T-mixer, in the whole range of Re used to characterize the flow. Andreussi et al [17] investigated different flow regimes occurring in T-mixers using direct numerical simulations. Different values of the aspect ratio of the inlet channels (width to height ratio) was considered and the results show that all the critical values of the Reynolds number, at which the transitions between the different regimes occur, were found to be very similar for aspect ratio of 0.75 and 1, but this scenario is completely different for aspect ratio 2 and in this case, the flow has a vorticity dynamics that is significantly different from those observed for the other aspect ratios.…”

Density effect on the mixing efficiency and flow modes in T-shaped micromixers

“…Thus, flow regimes depending on the Reynolds number were investigated in many works [4,5]. At that, quite an interesting hydrodynamic phenomenon, namely the flow reversal or engulfment flow regime [5][6][7][8] upon reaching the critical Reynolds number of 130-160 was observed in the T-shaped mixer. The aim of the present work is a systematic study of the effects of miscible fluids densities ratio on the flow and mixing regimes in the T-shaped micromixer.…”