Evaluation of Mass Transfer Capability in Viscoelastic Electrolyte Solutions on a Perfect Ion-Selective Membrane

Abstract

Ion-selective properties are widely used in desalination, energy storage in batteries, electroplating, etc. This paper presents a direct numerical simulation (DNS) of electroconvection (EC) in polymer electrolyte solutions on a perfectly selective membrane surface (PSMS), considering the Weissenberg effect and Joule heating. Different polymer elasticities on PSMS mass transfer are investigated in detail, including the instantaneous evolution, morphology structure, elasticity mechanism for transport capability, and global assessment. The results reveal that polymer electrolytes promote the formation of small vortices (low flux) and merge into a reduced number of large vortex structures (high flux). The crown and spike morphology of charge density and the mushroom-like morphology of salt concentration tend to be cloudier in the polymer electrolytes, with a marked decrease in injection height compared to that of Newtonian fluid. The streaks of strong polymer stretching reduce fluctuations with increased interface impedance in the extended space charge layer (ESCL), described by the first normal stress difference (N1) and the local Weissenberg number (Wil). The typical temperature difference is negatively correlated with the Wi numbers. The cumulative distribution function (CDF) and power spectral density (PSD) are characterized by an effective enhancement of the system stability, reducing the ion mass transfer and reaching a maximum of 45%. The polymer solution allows a more stable cation passage or deposition than Newtonian media at the same flux rate on the selective membrane.

Keywords: Ion selective membrane, mass transfer, Electrohydrodynamic, Polymer, Viscoelastic fluid.