Vortex-induced particle capture in a micro cross-shaped channel.

• The motion and capture of spherical particles in a micro cross-shaped channel are studied. • The orbital motion of finite-size particles within confined vortex is revealed. • The window of particle capture is modified by unsteady engulfment flows. Vortex-induced particle capture has attracted widespread attention as an effective tool for particle preconcentration or manipulation. In this work, the motion and capture of particles in confined vortices in a micro cross-shaped channel are explored by a high-speed camera within Reynolds numbers ranging from 10 to 450. Micro Laser-Induced Fluorescence (μLIF) and numerical simulation are used to visualize flow structures. Results demonstrate that a buoyant particle undergoes an attenuation oscillation, finally arriving a periodic orbit (i.e., a limit cycle) inside the vortex. The formation of the orbit is closely associated with the development of recirculating flows in the microchannel. With an increase in the number of captured particles, the average distributions of particles show particle exchange corridors between capture regions and mainstream, which is caused by interactions between particles or flow instability. Once the particle density exceeds the fluid density, the particle periodic orbits disappear, and particles move directly or spirally to the outlets. Moreover, oscillation induced by vortex merging and splitting influences the quantities and distributions of capture regions, as well as the migration paths of buoyant particles. In addition to particle capture at the channel center, a portion of captured particles is observed near channel walls. [ABSTRACT FROM AUTHOR]