Self-ordering and organization of in-line particle chain in a square microchannel

Abstract

Precise determination of microfluidic behaviors is theoretically significant and has shown remarkable application prospects. This work numerically studies the self-ordering and organization of an in-line particle chain flowing through a square microchannel. The immersed boundary-lattice Boltzmann method is employed, and effects of particle Reynolds number (Rep), length fraction (⟨Lf⟩, characterizes particle concentration), and particle size are focused. Results imply a relatively complex migration of small-particle chains. Three typical states are observed, that is, the equilibrium position finally in a stabilized, fluctuated, or chaotic condition. The corresponding dynamic processes are presented. Interestingly, how interparticle spacing evolves with time shows similar regularity with the three states, corresponding to a particle chain either being evenly distributed, moving like a bouncing spring, or continuously in disordered motions. The flow field and force conditions are analyzed to clarify the mechanisms, suggesting the subtle interaction among vortex-induced repulsive force, wall-induced lift force, and shear gradient lift force is the reason behind. Based on different states, migratory patterns are categorized as Stable Pattern, Spring Pattern, and Chaotic Pattern, and an overall classification is also obtained. Moreover, effects of Rep and ⟨Lf⟩ are identified, where a rising Rep leads to an equilibrium position toward the wall and larger volatility of interparticle spacings. The dynamic characteristics are characterized by lagging, translational, and angular velocities of particles in the chain. Finally, a contrastive study of large particles is performed. The present investigation is expected to provide insight into regularities of in-line particle chains and possible applications.