Abstract
The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration.
Highlights
Micromixers—constituted by channels having a hydraulic diameter below or equal to1 mm—have been widely proposed in the past years for liquid mixing because they allow continuous operation with exceptional control over transport phenomena and residence time
The passive-scalar concentration field along different crosssections in the mixer geometry, the flow streamlines, and the vortical structures identified through the isocontour of the vortex indicator λ2 [84] are shown for the T-shaped microjunction (TJ) case and for the TJC case
It is reasonable to infer that the physical mechanism triggering mixing with cavities and the interplay between the recirculation embedded in the cavity region and the vortical structures formed in the different flow regimes of the T-shaped micro-junction still holds for different mixing channel cross-sections
Summary
1 mm—have been widely proposed in the past years for liquid mixing because they allow continuous operation with exceptional control over transport phenomena and residence time. Working in continuous flow reduces the accumulation of reactive or toxic intermediates, and the high surface-to-volume ratio provides enhanced heat transfer capacity granting safer operation with highly exothermic reactions, expanding the number of feasible reactions that can be performed and intensified [1–5]. One of the main disadvantages in the use of micromixers is that liquid mixing has to take place in laminar flow regimes for typical low Reynolds numbers, mixing needs to be enhanced by exploiting active or passive methods [10–14]. The active methods apply outsourced energy, such as ultrasound, pressure pulse, and electric and magnetic fields [15–19]. The passive ones, instead, promote mixing by devising a clever geometry of the micromixers aimed at breaking the flow symmetries without any external energy input
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