Impact of cross-sectional geometry on mixing performance of spiral microfluidic channels characterized by swirling strength of Dean-vortices

Abstract

Mixing in a microfluidic system is challenging due to dominant diffusion effects at a microscale (low Reynolds number). In this work, we report the improvement of mixing performance in spiral microchannels of varying cross-sectional geometry and hydraulic diameter. The formation of secondary flow interactions in spiral channels, known as Dean vortices, aid the primary diffusion process. The evolution of these Dean vortices was experimentally visualized along the length of the microchannel by confocal microscopy, and then compared to numerical studies. The cross-sectional geometries of the spiral channels, especially in the case of irregular shapes such as the semi-circular and trapezoidal profiles, were found to be an important factor in tuning the strength of Dean vortices, which in turn dictate the mixing performance, as opposed to diffusion which is more prominent at lower Re. This experiment-based finding has been validated via the evaluation of swirling strength of the working fluid, obtained using a numerical study. The results thus obtained show a mixing performance greater than 90% above a Reynolds number of 20 for most spiral channel designs, making this system suitable for high throughput operation with reduced pressure drop. This work is the first to experimentally and numerically demonstrate, within this operating range (20 < Re < 277), the impact on mixing performance in curved microchannels of varying cross-sectional geometries of constant cross-sectional area, and of varying hydraulic diameters for square shaped channels. The capability of these channels to operate at a moderately high Re with enhanced mixing performance and reduced pressure drop would be of great use in large-scale industrial operations, such as complex integrated micro-reactors wherein pressure drop plays a key role.

Expandable Polymer Assisted Wearable Personalized Medicinal Platform

“…It can be clearly observed that circular channel provided better mixing than the rectangular microchannel mixer since the complete mixing reaching a concentration of 50 mol m − ³ was reached at a lower unit number than the rectangular channel‐based mixer. This result has also confirms with what has been reported in other studies such as the one reported by Balasubramaniam et al [ 31 ] The study has shown that channels with circular cross sectional profile affect the strength of the produced Dean vortices which enhances the diffusion process of mixing. [ 31 ] Figure 4e,f shows the corresponding simulation results (e) design and concentration profiles of the rectangular‐shaped microchannel mixer and (f) design and concentration profiles of the circular‐shaped microchannel mixer, along the mixers units.…”

“…This result has also confirms with what has been reported in other studies such as the one reported by Balasubramaniam et al [ 31 ] The study has shown that channels with circular cross sectional profile affect the strength of the produced Dean vortices which enhances the diffusion process of mixing. [ 31 ] Figure 4e,f shows the corresponding simulation results (e) design and concentration profiles of the rectangular‐shaped microchannel mixer and (f) design and concentration profiles of the circular‐shaped microchannel mixer, along the mixers units. Since the goal is for the platform to enable mixing, it was important to study the capability of the mixer of mixing fluids of various viscosities.…”

Enhanced inertial focusing of microparticles and cells by integrating trapezoidal microchambers in spiral microfluidic channels

“…Curved channels induce a Dean ow 33,34 that appears as two counter-rotating vortices located in the lower and upper halves of the channel cross section. [35][36][37] Nivedita et al 32 described the essential forces and uid dynamics involved in microparticles focusing inside a Dean ow, in reference to Dean's original work in 1928, 38 they stated that the maximum velocity point shis from the centre towards the outer (concave) wall inducing a sharp velocity prole that increases pressure leading to a uid recirculation known as Dean vortices. The Dean force acting on particles depends mainly on particle diameter and ow velocity and becomes dominant to inertial forces in smaller particle diameters.…”

Numerical investigation of the performance of 3D‐helical passive micromixer with Newtonian fluid and non‐Newtonian fluid blood

“…They found that the mixing performance improved for high Reynolds number (Re > 10); however, there was not much significant difference in the mixing index at low Reynolds number (Re < 10). Balasubramaniam et al 20 experimentally and numerically examined the mixing behavior of Newtonian fluids for an in‐plane spiral shape mixer with different cross‐sectional geometries, namely, square, semicircular, rectangular, and trapezoidal. Employing semicircular and trapezoidal cross‐sections showed notable improvement in the mixing index without much change in the pressure drop of the micromixer.…”