T-shaped micro-mixer: engulfment regime

The importance of micro-scale devices in chemical engineering has increased significantly during the last years. The smaller characteristic dimensions in microscale devices leads to extremely high surface-to-volume ratio, which in turn provides several advantages over conventional-size reactors, mixers and heat transfer equipments, such as (a) higher transport (e.g., heat and mass transfer) rates, (b) safe environment for hazardous or toxic chemicals (due to low amount of chemicals used during the process), etc…

The performance of most micro-chemical devices strongly depends on the efficiency of mixing, especially when dealing with fast reactions. The information on flow characteristics and pressure drop correlations is still discussed controversially in the literature, so a systematic detailed analysis is needed.

T-shaped micromixers are commonly used in microfluidics to promote mixing between two fluid streams; in this type of applications, two streams enter from the two opposite channels (inlet channels) and the mixture exit from the third channel (outflow channel). Such configurations are also often found as junction elements in complex micro-systems.

The flow in micro T-mixers is characterized by different regimes, whose onset depends on different parameters, such as the Reynolds number, the mixer geometry, and the inflow conditions. 

We focus our study on the engulfment regime, where an organized and stationary pattern of vortical  structures is observed, which breaks the flow symmetries and makes fluid elements of one stream reach the opposite side of the mixing channel. This clearly leads to a significantly larger mixing than in the other regimes.

We used DNS and linear stability analysis to investigate the onset of the engulfment regime.

Related publications:

Andrea Fani, Simone Camarri, Maria Vittoria Salvetti: Investigation of the steady engulfment regime in a three-dimensional T-mixer. In: Physics of Fluids, 25 (6), pp. 064102, 2013, ISSN: 10706631.