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Electrokinetic Instability Mechanism of Double-layered Miscible Fluids with Different Electrolyte Concentrations in DC Electric Field

J.W. Park, K.H. Kang and K.Y. Huh
Pohang University of Science and Technology, KR

Keywords: electrokinetic instability, electroosmotic flow, concentration difference

Interfacial instability has recently been observed for DC-powered electroosmotic flow by Chen and Santiago [1]. So far, no plausible explanation has yet been made since the phenomenon is contrary to common belief of laminar flow at extremely small Reynolds number. In the present work we are showing numerically that the instability results as a consequence of polarized ionic species with a conductivity gradient. It is similar in nature to the so-called electrohydrodynamic instability phenomenon. Simulation is performed in a two-dimensional straight channel, under the Nernst-Planck's framework of electrochemical systems. The Navier-Stokes equation with the Coulombic body force, the ion transport equation and Poisson equation under electroneutrality assumption were discretized using finite volume method. The result shows an impressive agreement of the calculated concentration profile with the photographic images in Chen and Santiago [1]. Detailed discussions on the instability mechanism will be made on the basis of the numerical results for flow field, electric field, and concentration distributions. Instability criteria may also be determined from the parametric study. [1] C. H. Chen and J. G. Santiago (2002) ''Electrokinetic flow instability in high concentration gradient microflows,'' Proc. 2002 Int'l Mech. Eng. Cong. and Exp., New Orleans, LA, CD vol.1, Paper No. 33563.

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