Abstract
In this work, the inertial focusing of a microparticle in spiral channels is investigated numerically using a numerical solver developed in the framework of OpenFOAM open-source software. A special periodic boundary condition was implemented for a developed immersed boundary method to mimic the long microchannel, along with an adaptive meshing procedure to significantly reduce memory resources and shorten computation time. Simulation of a microparticle moving inside a square duct confirmed the existence of eight equilibrium positions over the channel’s cross section, four of which are located close to the channel wall centers, whereas the others are positioned near the corners, which has been reported in many studies before. Most importantly, we present, for the first time, a direct numerical simulation for the inertial sorting phenomenon of a microparticle in the spiral channel of rectangular and trapezoidal cross sections. Comprehensive analysis of the resulting lateral force field maps and Dean vortex configurations provides more insight into the focusing mechanism of a microparticle, which is beneficial for the design and optimization of cell separation microfluidic devices.
Highlights
Over the last few years, inertial microfluidics has gained increasing attention and found its application in various lab-on-chip devices for particle manipulation
We consider the motion of a spherical particle of diameter d = 0.65 mm in a pressure-driven flow of an incompressible Newtonian fluid through a straight channel
The additional Corner Equilibrium Position (CEP) were reported in experiments and numerical simulations using the immersed boundary (IB) method.6,23. It can be observed from the lateral force profile that the particle approaches the CEP only if its initial position is on the diagonal of the cross section, whereas any other starting point leads to the focusing toward either two Face Equilibrium Positions (FEPs)
Summary
Over the last few years, inertial microfluidics has gained increasing attention and found its application in various lab-on-chip devices for particle manipulation. The shear-gradient lift force, Fs, is formed due to the curvature of the velocity profile near the particle and tends to direct the particle away from the channel center, whereas the wall-induced lift force, Fw, repels the particle away from the wall The combination of these two forces forms a lateral force field that drives the particle toward the equilibrium position. Di Carlo et al. used the finite element method to find that the shear-gradient lift scales as Fs ∼ (d3/H) and the wall-induced lift scales as Fw ∼ (d6/H4), with d being the particle diameter and H being the channel height These results were obtained for the particle of relatively small size, 0.05 < d/H < 0.2, at a moderate Reynolds number (Re). This problem causes serious difficulty for conventional modeling methods, using body-fitted mesh, in handling moving mesh Because of this difficulty, previous studies relied on modeling fluid flows only in the analysis of focusing behavior of the particle explicitly.. For the first time, we show the direct simulation for the inertial focusing process of a microparticle in the spiral microchannel
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