Inertial focusing in a straight channel with asymmetrical expansion–contraction cavity arrays using two secondary flows

Abstract

G. (2013). Inertial focusing in a straight channel with asymmetrical expansion-contraction cavity arrays using two secondary flows. Journal of Micromechanics and Microengineering, 23 (8), 1-13. Inertial focusing in a straight channel with asymmetrical expansioncontraction cavity arrays using two secondary flows AbstractThe focusing of particles has a variety of applications in industry and biomedicine, including wastewater purification, fermentation filtration, and pathogen detection in flow cytometry, etc. In this paper a novel inertial microfluidic device using two secondary flows to focus particles is presented. The geometry of the proposed microfluidic channel is a simple straight channel with asymmetrically patterned triangular expansion-contraction cavity arrays. Three different focusing patterns were observed under different flow conditions: (1) a single focusing streak on the cavity side; (2) double focusing streaks on both sides; (3) half of the particles were focused on the opposite side of the cavity, while the other particles were trapped by a horizontal vortex in the cavity. The focusing performance was studied comprehensively up to flow rates of 700 μl min−1. The focusing mechanism was investigated by analysing the balance of forces between the inertial lift forces and secondary flow drag in the cross section. The influence of particle size and cavity geometry on the focusing performance was also studied. The experimental results showed that more precise focusing could be obtained with large particles, some of which even showed a single-particle focusing streak in the horizontal plane. Meanwhile, the focusing patterns and their working conditions could be adjusted by the geometry of the cavity. This novel inertial microfluidic device could offer a continuous, sheathless, and high-throughput performance, which can be potentially applied to high-speed flow cytometry or the extraction of blood cells. (1) single focusing streak on cavity side; (2) double focusing streaks on both sides; (3) half of particles focused on the opposite side of cavity, and other particles trapped by horizontal vortex in cavity. The focusing performance was studied comprehensively up to the flow rates of 700 µl min -1 . The focusing mechanism was investigated by analyzing force balance between inertial lift forces and secondary flow drag in the cross section.The influence of particle size and cavity geometry on the focusing performance was also studied. Experimental results showed that a more pronounced focusing performance can be obtained with large particles, which even showed a single-particle focusing streak in horizontal plane. Meanwhile, focusing patterns and their working conditions were adjustable by the geometry of cavity. The novel inertial microfluidic device was capable of offering a continuous, sheathless, and high-throughput performance, which can be potentially applied to highspeed flow cytometry or extraction of blood cells.

Inertial effects on the generation of co-laminar flows

“…The recirculating eddies formed in such geometries have been shown to induce the formation of biofilm streamers when certain strains of bacteria are introduced . Similar phenomena can be observed in contracting or expanding flows, which also have been shown to induce out-of-plane flow (Shankar 2000;Zhang et al 2013). In the case of the inlet geometry considered here, velocity gradients between the centreline of the channel and the wall drives flow out of plane, further enhancing mixing as shown in figure 7.…”

Fundamentals and applications of inertial microfluidics: a review

“…straight 42,44,49,54 , straight channel with pillar arrays 26,97,111 or expansion-contraction arrays 25,79,82 , spiral 77,112,113 , and serpentine 43,106,114 . These inertial microfluidic devices have been widely explored for their applications in biomedicine and industry, such as extraction of blood plasma 80,107 Although there have been extensive investigations on the mechanism of particle inertial focusing, and a variety of applications on particle/cell separation have been demonstrated, quantitative design rules are still lacking for particle inertial manipulation in different shaped channels.…”

“…The secondary flow usually appears in a curved channel 23 or a straight channel with disturbance obstacles [24][25][26] . In a curved channel, the secondary flow is induced by a pressure gradient in the radial direction, because of fluid momentum mismatch in the centre and nearwall region within the curvature 4 .…”

Inertial Focusing in Microfluidics

“…This behavior results from vortices that form in the expanded side sections, as shown in Figure 4 c (64–66). Despite larger particles being equilibrated farther from the wall, the disappearance of the wall interaction force allows for much greater migration distances compared with those of smaller particles, enabling separation (65, 67, 68). In some device designs, this interaction can actually trap the larger particles within the expanded-section vortices (69).…”