Critical selection of shear sheltering in electroconvective flow from chaotic to steady state

Ion and water are transported by electroconvection near permselective membranes, resulting in complex phenomena associated with the flow-fines interaction. Sheltering the flow chaos by the shear flow is a common strategy in plasma fluids and has recently been successfully applied to control ionic fluids. The paper herein reveals the critical selection of shear velocity regarding the fluid from a chaotic to a steady state through numerical and theoretical analyses. For the shear sheltering, the dimensionless Debye length lambda(D) with varying channel height is introduced to achieve a comprehensive discussion of the factors and laws affecting the shear vortex state. Based on an analysis of the vortex driving mechanism, the scaling of the slip velocity u(s) similar to (lambda(-1)(D) Delta phi(4))(1/3) is recommended as the critical selection factor for the steady and chaotic state under a fixed shear flow velocity, which involves the dimensionless Debye length lambda(D) and voltage difference Delta phi. Furthermore, for ionic fluid control by shear flow, a critical shear velocity U-HPC is proposed to distinguish the electroconvective flow from a chaotic state to a steady state. When the shear flow velocity U-HP > U-HPC, the shear flow shelters chaos, and the scaling law is also recommended for the regulation of the critical shear flow velocity U-HPC jointly by lambda(D) and Delta phi. The analysis is confirmed by direct numerical simulation and existing experimental data (J. Fluid Mech, vol. 813, 2017, pp. 799-823). This work provides a more comprehensive physical insight for shear sheltering and affects the design of electromembrane microfluidics.

Automated summary

This paper reveals the critical selection of shear velocity regarding the fluid from a chaotic to a steady state through numerical and theoretical analyses. It introduces the dimensionless Debye length and voltage difference to achieve a comprehensive discussion of the factors affecting the shear vortex state. Furthermore, a critical shear velocity is proposed to distinguish the electroconvective flow from a chaotic state to a steady state for ionic fluid control by shear flow.