The different flow regimes occurring for increasing Reynolds numbers (Re) in an arrow-shaped micro-mixer operated for liquid mixing are investigated by the synergic use of experimental flow visualizations and direct numerical simulations. The tilting angle of the arrow-mixer inlet channels with respect to those of the T-shaped mixer is alpha = 20 degrees. Consistent with previous studies in the literature, it is found that the onset of the engulfment regime, and consequently the sharp increase of the degree of mixing between the two flow streams, occurs at a lower Reynolds number than for a T-mixer operating in the same conditions. However, in contrast to what is observed for T-mixers, the degree of mixing does not increase monotonically with Re. In fact, at approximately Re = 150, based on the inlet bulk velocity and the hydraulic diameter of the mixing channel, there is a drop of the mixing degree. This is due to a change in the topology of the vorticity field and, in particular, to the presence of a unique vortical structure in the mixing channel instead of two corotating ones typical of the engulfment regime. By further increasing the Reynolds number, the vortical structure in the mixing channel grows in size and eventually starts to oscillate, leading again to an increase of the degree of mixing, starting from Re similar or equal to 170. Additional simulations have been carried out in order to investigate the sensitivity to the tilting angle of the inlet channels, namely for alpha= 10 degrees, 15 degrees, 25 degrees. As expected, it is found that the value of Re at which the engulfment regime occurs decreases with increasing a. Then, for alpha = 10 degrees and 15 degrees, the degree of mixing monotonically increases with the Reynolds numbers and the flow topology in the whole engulfment regime is practically the same as for T-mixers. Conversely, the configuration with alpha = 25 degrees shows a behavior of mixing and of flow features with increasing Reynolds number very similar to those observed for alpha= 20 degrees.

Steady flow regimes and mixing performance in arrow-shaped micro-mixers

Mariotti, A.;Galletti, C.
;
Brunazzi, E.
;
Salvetti, M. V.
2019-01-01

Abstract

The different flow regimes occurring for increasing Reynolds numbers (Re) in an arrow-shaped micro-mixer operated for liquid mixing are investigated by the synergic use of experimental flow visualizations and direct numerical simulations. The tilting angle of the arrow-mixer inlet channels with respect to those of the T-shaped mixer is alpha = 20 degrees. Consistent with previous studies in the literature, it is found that the onset of the engulfment regime, and consequently the sharp increase of the degree of mixing between the two flow streams, occurs at a lower Reynolds number than for a T-mixer operating in the same conditions. However, in contrast to what is observed for T-mixers, the degree of mixing does not increase monotonically with Re. In fact, at approximately Re = 150, based on the inlet bulk velocity and the hydraulic diameter of the mixing channel, there is a drop of the mixing degree. This is due to a change in the topology of the vorticity field and, in particular, to the presence of a unique vortical structure in the mixing channel instead of two corotating ones typical of the engulfment regime. By further increasing the Reynolds number, the vortical structure in the mixing channel grows in size and eventually starts to oscillate, leading again to an increase of the degree of mixing, starting from Re similar or equal to 170. Additional simulations have been carried out in order to investigate the sensitivity to the tilting angle of the inlet channels, namely for alpha= 10 degrees, 15 degrees, 25 degrees. As expected, it is found that the value of Re at which the engulfment regime occurs decreases with increasing a. Then, for alpha = 10 degrees and 15 degrees, the degree of mixing monotonically increases with the Reynolds numbers and the flow topology in the whole engulfment regime is practically the same as for T-mixers. Conversely, the configuration with alpha = 25 degrees shows a behavior of mixing and of flow features with increasing Reynolds number very similar to those observed for alpha= 20 degrees.
2019
Mariotti, A.; Galletti, C.; Brunazzi, E.; Salvetti, M. V.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/991773
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