Inertial focusing in triangular microchannels with various apex angles

Jeong-Ah Kim; Aditya Kommajosula; Yo-Han Choi; Je-Ryung Lee; Eun-Chae Jeon; Baskar Ganapathysubramanian; Wonhee Lee

doi:10.1063/1.5133640

Inertial focusing in triangular microchannels with various apex angles

Biomicrofluidics. 2020 Mar 24;14(2):024105. doi: 10.1063/1.5133640. eCollection 2020 Mar.

Authors

Jeong-Ah Kim¹, Aditya Kommajosula², Yo-Han Choi³, Je-Ryung Lee⁴, Eun-Chae Jeon⁵, Baskar Ganapathysubramanian², Wonhee Lee

Affiliations

¹ Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea.
² Department of Mechanical Engineering, Iowa State University (ISU), Ames, Iowa 50011, USA.
³ Graduate School of Nanoscience and Technology, KAIST, Daejeon 34141, South Korea.
⁴ Department of Electronics and Information Engineering, Korea University, Sejong 30019, South Korea.
⁵ School of Materials Science & Engineering, University of Ulsan, Ulsan 44610, South Korea.

Abstract

We consider inertial focusing of particles in channels with triangular cross sections. The number and the location of inertial focusing positions in isosceles triangular channels can change with varying blockage ratios (a/H) and Reynolds numbers (Re). In triangular channels, asymmetric velocity gradient induced by the sloped sidewalls leads to changes in the direction and the strength of the inertial lift forces. Therefore, varying the configuration (specifically, angle) of the triangular cross section is expected to lead to a better understanding of the nature of the inertial lift forces. We fabricated triangular microchannels with various apex angles using channel molds that were shaped by a planing process, which provides precise apex angles and sharp corners. The focusing position shift was found to be affected by the channel cross section, as expected. It was determined that the direction of the focusing position shift can be reversed depending on whether the vertex is acute or obtuse. More interestingly, corner focusing modes and splitting of the corner focusing were observed with increasing Re, which could explain the origin of the inertial focusing position changes in triangular channels. We conducted fluid dynamic simulations to create force maps under various conditions. These force maps were analyzed to identify the basins of attraction of various attractors and pinpoint focusing locations using linear stability analysis. Calculating the relative sizes of the basins of attractions and exhaustively identifying the focusing positions, which are very difficult to investigate experimentally, provided us a better understanding of trends in the focusing mechanism.