title: Electrokinetic mixing at high zeta potentials: ionic size effects on cross stream diffusion.
abstract: The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer. The method consists of a finite difference based numerical approach for non-uniform grid which is applied to the dimensionless form of the governing equations, including the modified Poisson-Boltzmann equation. The results reveal that, neglecting the ionic size at high zeta potentials gives rise to the overestimation of the mixing length, because the steric effects retard liquid flow, thereby enhancing the mixing efficiency. The importance of steric effects is found to be more intense for channels of smaller width to height ratio. It is also observed that, in sharp contrast to the conditions that the ions are treated as point charges, increasing the zeta potential improves the cross stream diffusion when incorporating the ionic size. Moreover, increasing the EDL thickness decreases the mixing length, whereas the opposite is true for the channel aspect ratio.
authors.affiliation: Center of Excellence in Energy Conversion (CEEC), School of Mechanical Engineering, Sharif University of Technology, Tehran 11155-9567, Iran. Electronic address: ar_ahmadianyazdi@mech.sharif.edu.
authors.forename: Alireza
authors.initials: A
authors.lastname: Ahmadian Yazdi
authors.affiliation: Department of Mechanical Engineering, University of Kurdistan, Sanandaj 66177-15175, Iran. Electronic address: a.sadeghi@eng.uok.ac.ir.
authors.forename: Arman
authors.initials: A
authors.lastname: Sadeghi
authors.affiliation: Center of Excellence in Energy Conversion (CEEC), School of Mechanical Engineering, Sharif University of Technology, Tehran 11155-9567, Iran. Electronic address: saman@sharif.edu.
authors.forename: Mohammad Hassan
authors.initials: MH
authors.lastname: Saidi
mesh_terms: D004058:Diffusion; D053841:Electroosmosis / Q000295:instrumentation*; D004867:Equipment Design; D007477:Ions / Q000737:chemistry*; D007700:Kinetics
chemical_list: D007477:Ions
keywords: Electroosmotic flow; Micromixer; Steric effects