CFD analysis of electroviscous effects in electrolyte liquid flow through heterogeneously charged uniform microfluidic device

Abstract

This study has numerically investigated the charge-heterogeneity effects in the electroviscous flow of symmetric ($1$:$1$) electrolyte liquid through a uniform slit microfluidic device. The Poisson's, Nernst-Planck (N-P), Navier-Stokes (N-S), and continuity equations are solved using the finite element method (FEM) to obtain the flow fields, such as total electrical potential ($U$), excess charge ($n^{\ast }$), induced electric field strength ($E_{\text{x}}$), and pressure ($P$) fields for following conditions: inverse Debye length ($2\le K\le 20$), surface charge density ($4\le S_{\text{1}}\le 16$), and surface charge-heterogeneity ratio ($0\le S_{\text{rh}}\le 2$). Results have shown that the total potential ($|\Delta U|$) and pressure ($|\Delta P|$) drop maximally increase by 99.09% (at $K=20$, $S_{\text{1}}=4$) and 12.77% (at $K=2$, $S_{\text{1}}=8$), respectively with overall charge-heterogeneity ($0\le S_{\text{rh}}\le 2$). Electroviscous correction factor (i.e., the ratio of effective to physical viscosity) maximally enhances by 12.77% (at $K=2$, $S_{\text{1}}=8$), 40.98% (at $S_{\text{1}}=16$, $S_{\text{rh}}=1.50$), and 41.35% (at $K=2$, $S_{\text{rh}}=1.50$), with the variation of $S_{\text{rh}}$ (from 0 to 2), $K$ (from 20 to 2), and $S_{\text{1}}$ (from 0 to 16), respectively. Further, a simple pseudo-analytical model is developed to estimate the pressure drop in the electroviscous (EV) flow, accounting for the influence of charge-heterogeneity based on the Poiseuille flow in the uniform channel. This model predicts the pressure drop $\pm$2-4% within the numerical results. The robustness and simplicity of this model enable the present numerical results for engineering and design aspects of microfluidic applications.

46 pages, 17 figures

References in corpus (4)

• Liquid friction on charged surfaces: from hydrodynamic slippage to electrokinetics
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• CFD analysis of electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged non-uniform microfluidic device
• CFD analysis of the influence of contraction size on electroviscous flow through the slit-type non-uniform microfluidic device