# Particle Segregation and Dynamics in Confined Flows

Entry: Chia Wei Hsu, AP 225, Fall 2010

D. Di Carlo, J. F. Edd, K. J. Humphry, H. A. Stone, and M. Toner, "Particle Segregation and Dynamics in Confined Flows," Phys Rev Lett **102**, 094503 (2009)

## Summary

Rigid spherical particles exhibit lateral migration in cylindrical pipes. Such phenomenon cannot be explained by the Stokes equation (ie. linearized Navier-Stokes equation at low Reynolds number). Thus the inertial contribution of the particles must be taken into account, and the full Navier-Stokes equations must be used. In order to simplify the complexity of this problem, previous studies have focused on cases when particles dimension (<math>a</math>) is much smaller than the channel cross section dimension (<math>H</math>). In this paper, the authors show that such "point-particle" approximation is not valid when <math>a</math> approaches <math>H</math>.

## Method

The authors examine rectangular cross-section microchannels. They compare experimental observations with numerical calculations based on finite element method.

The experimental system is prepared using soft-lithography fabrication. They consist of microchannels (length 5 cm; width and height 20-50 µm) with dilute polystyrene particles (<math>a</math>=5-20 µm) suspended in water. The polystyrene particles flow at controlled rates using a syringe pump.