Dean Flow Dynamics in Low-Aspect Ratio Spiral Microchannels

Abstract

A wide range of microfluidic cell-sorting devices has emerged in recent years, based on both passive and active methods of separation. Curvilinear channel geometries are often used in these systems due to presence of secondary flows, which can provide high throughput and sorting efficiency. Most of these devices are designed on the assumption of two counter rotating Dean vortices present in the curved rectangular channels and existing in the state of steady rotation and amplitude. In this work, we investigate these secondary flows in low aspect ratio spiral rectangular microchannels and define their development with respect to the channel aspect ratio and Dean number. This work is the first to experimentally and numerically investigate Dean flows in microchannels for Re > 100, and show presence of secondary Dean vortices beyond a critical Dean number. We further demonstrate the impact of these multiple vortices on particle and cell focusing. Ultimately, this work offers new insights into secondary flow instabilities for low-aspect ratio, spiral microchannels, with improved flow models for design of more precise and efficient microfluidic devices for applications such as cell sorting and micromixing.

Scaling laws in axisymmetric magnetohydrodynamic duct flows

“…Large convective rolls are observed on both side of the mid-horizontal plane. The latter are generically referred as Dean rolls in the literature [19][20][21] , and play a part in the generation of the Shercliff layers at the conducting walls. As is clear in Fig.…”

Analysis of a microreactor for synthesizing nanocrystals by computational fluid dynamics

“…Curvature also generates centripetal forces directing the fluid to a curvilinear motion. These two forces, combined with wall friction, result in Dean forces that produce a double symmetric vortex structure perpendicular to the main flow direction . For small flow rates, Figure shows the vortices are generated at the first half of each curved segment at the mixing section, but is destroyed at the other half as inertial forces change to the opposite direction and counterbalance centripetal and friction forces.…”

“…These two forces, combined with wall friction, result in Dean forces that produce a double symmetric vortex structure perpendicular to the main flow direction. [35] For small flow rates, Figure 6 shows the vortices are generated at the first half of each curved segment at the mixing section, but is destroyed at the other half as inertial forces change to the opposite direction and counterbalance centripetal and friction forces. On the other hand, for higher flow rates the vortex dynamics is sustained through the whole mixing section and impacts mixing quality as will be discussed in the next section.…”

On‐Chip Generation of Vortical Flows for Microfluidic Centrifugation

“…• Bend [40] • Serpentine [41][42][43][44] • Spiral [45][46][47] • Alternating symmetry (e.g., zigzag) [48] Simple, effective, and potentially low-cost Considerable pressure drop necessitates large benchtop pumps to drive the flow Not possible to tune centrifugation intensity independent of flow for a given device Dead volumes around corners in cavities, chambers, and sharp bends/turns can lead to particle deposition and fouling…”