Axial and lateral particle ordering in finite Reynolds number channel flows

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Original entry by Sagar Bhandari, APPHY 225 Fall 2010

Reference

Axial and lateral particle ordering in finite Reynolds number channel flows, Katherine J. Humphry, Pandurang M. Kulkarni, David A. Weitz, Jeffrey F. Morris and Howard A. Stone, Physics of Fluids, 22, 081703 (2010)

Keywords

axial, lateral, particle order, reynolds, microfluidic

Summary

In case of rectangular cross section microfluidic channel and particle size comparable to the channel size, consequences of the combination of confining geometries, inertia, and particle concentration have not been characterized. In this paper, the authors study the effects of particle concentration and channel geometry on inertial focusing. The authors find that the location and number of focusing positions depend on the linear number density of particles along the channel. The linear number density is a function of channel cross section and number of particles. 6 cm long microfluidic channels with a uniform rectangular cross-section in PDMS are used in their experiment. Polystyrene beads of diameter d=9.9 um are dispersed in water. As shown in Fig 1 , the particles, initially randomly located, migrate in the directions transverse to the flow and settle in characteristics focusing positions and spacings.

Figure 1:

Sagar wiki4 image1.jpg



Figure 2:

Sagar wiki4 image2.jpg

Using simulations to investigate the mechanism for this regular spacing , the authors find that confinement in the channel leads to fixed points in the flow with respect to the particle, and these roughly define the positions of neighboring particles in the axial direction. They infer "inertially influenced hydrodynamic interaction" as the source for this kind of behavior.