Coupling between Buoyancy Forces and Electroconvective Instability near Ion-Selective Surfaces

Abstract

Recent investigations have revealed that ion transport from aqueous electrolytes to ion-selective surfaces is subject to electroconvective instability that stems from coupling of hydrodynamics with electrostatic forces. These systems inherently involve fluid density variation set by salinity gradients. However, the coupling between the buoyancy effects and electroconvective instability has not yet been investigated although a wide range of electrochemical systems are naturally prone to these interplaying effects. In this study we thoroughly examine the interplay of gravitational convection and chaotic electroconvection. Our results reveal that buoyant forces can significantly influence the transport rates, otherwise set by electroconvection, when the Rayleigh number Ra of the system exceeds a value Ra∼1000. We show that buoyancy forces can significantly alter the flow patterns in these systems. When the buoyancy acts in the stabilizing direction, it limits the extent of penetration of electroconvection, but without eliminating it. When the buoyancy destabilizes the flow, it alters the electroconvective patterns by introducing upward and downward fingers of respectively light and heavy fluids.

Influence of Rayleigh-Bénard convection on electrokinetic instability in overlimiting current conditions

“…Movies showing the development of vortices in the system, along with the electrical response, for different configurations as well as of concentration profile (fluorescence lifetime) vs time are provided in the Supplemental Material [40]. These observations confirm the numerical predictions of Karatay et al [28]. It could not be determined in our case if the EKI vortices stayed counterrotating [9] or the RB flow caused corotating [41] or even helical [15] vortices.…”

“…Buoyancy mixing of the boundary layer near a membrane is known to decrease the mass transfer resistance [25][26][27]. Recently, direct numerical simulations to study the coupling of RB and EKI near a membranes have been performed [28]. The estimated currents were greatly influenced by the appearance of RB convection.…”

Stabilizing electrochemical interfaces in viscoelastic liquid electrolytes

“…S1. For these experiments, the cell is mounted in the gravitational stable position ( 22 , 37 ). We used current ramp measurements, which involved imposing a current on the electrolyte for a fixed period of time and recording the voltage response.…”

Transient electrohydrodynamic flow with concentration-dependent fluid properties: Modelling and energy-stable numerical schemes

“…Further, the effects of non-constant density and permittivity can be included in studies of electrokinetic instabilities beyond the Boussinesq approximation (see e.g. [66]). • The limitations of the model are (i) that we have assumed quasi-incompressibility (solenoidal velocity field), and (ii) that we have assumed isothermal flow.…”