title: Shear flow of an electrically charged fluid by ion concentration polarization: scaling laws for electroconvective vortices.
abstract: We consider electroconvective fluid flows initiated by ion concentration polarization (ICP) under pressure-driven shear flow, a scenario often found in many electrochemical devices and systems. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of ICP under shear flow: a unidirectional vortex structure, its height selection, and vortex advection. Determined by both the external pressure gradient and the electric body force, the dimensionless height of the sheared electroconvective vortex is shown to scale as (ϕ(2)/U(HP))(1/3), which is a clear departure from the previous diffusion-drift model prediction. To the best of our knowledge, this is the first microscopic characterization of ion concentration polarization under shear flow, and it firmly establishes electroconvection as the mechanism for an overlimiting current in realistic, large-area ion exchange membrane systems such as electrodialysis. The new scaling law has significant implications on the optimization of electrodialysis and other electrochemical systems.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Rhokyun
authors.initials: R
authors.lastname: Kwak
authors.affiliation: Singapore-MIT Alliance, National University of Singapore, Singapore 117576, Singapore.
authors.forename: Van Sang
authors.initials: VS
authors.lastname: Pham
authors.affiliation: Singapore-MIT Alliance, National University of Singapore, Singapore 117576, Singapore.
authors.forename: Kian Meng
authors.initials: KM
authors.lastname: Lim
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA and Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Jongyoon
authors.initials: J
authors.lastname: Han
mesh_terms: D053672:Electrochemotherapy / Q000295:instrumentation* / Q000379:methods*; D007477:Ions / Q000737:chemistry; D008567:Membranes, Artificial; D008962:Models, Theoretical; D033081:Shear Strength
chemical_list: D007477:Ions; D008567:Membranes, Artificial