Electrohydrodynamic linear stability of two immiscible fluids in channel flow

Department of Mechanical & Industrial Engineering , New Jersey Institute of Technology, Newark, New Jersey, United States
Electrochimica Acta (Impact Factor: 4.5). 04/2006; 51206585(85). DOI: 10.1016/j.electacta.2006.02.002


The electrohydrodynamic instability of the interface between two viscous fluids with different electrical properties in plane Poiseuille flow has recently found applications in mixing and droplet formation in microfluidic devices. In this paper, we perform the stability analysis in the case where the fluids are assumed to be leaky dielectrics. The two-layer system is subjected to an electric field normal to the interface between the two fluids. We make no assumption on the magnitude of the ratio of fluid to electric time scales, and thus solve the full conservation equation for the interfacial charge. The electric field is found to be either stabilizing or destabilizing, and the influence of the various parameters of the problem on the interface stability is thoroughly analyzed.

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Available from: P. G. Petropoulos, Dec 28, 2013
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    • "For a large wave number, the critical potential increases proportional to the square root of k. Ozen et al. [16] analyzed the linear stability of the interface between two immiscible fluids and found the effects of electric fields and mechanical properties to the instability of the interface. Moatimid and Obied Allah [17] investigated the linear surface wave instability between two finite fluid layers. "
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    ABSTRACT: This paper investigates analytically and experimentally electrohydrodynamic instability of the interface between two viscous fluids with different electrical properties under constant flow rates in a microchannel. In the three-dimensional analytical model, the two-layer system is subjected to an electric field normal to the interface between the two fluids. There is no assumption on the magnitude of the ratio of fluid to electric time scales, and thus the linear Poisson–Boltzmann equation are solved using separation of variable method for densities of bulk charge and surface charge. The electric field and fluid dynamics are coupled only at the interface through the tangential and normal interfacial stress balance equations. In the experiments, two immiscible fluids, aqueous NaHCO3 (the high electrical mobility fluid) and silicone oil (polydimethylsiloxane, the low electrical mobility fluid) are pumped into a microchannel made in polymethyl methacrylate) (PMMA) substrate. The normal electric field is added using a high voltage power supply. The results showed that the external electric field and increasing width of microchannel destabilize the interface between the immiscible fluids. At the same time, the viscosity of the high electrical mobility fluid and flow rates of fluids has a stabilizing effect. The experimental results and the analytical results show a reasonable agreement.
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    • "Comparing with a number of techniques (e.g., pressure, centrifuge, and thermal gradient driven flow), electroosmosis has been used to induce electroosmotic flow because electroosmosis does not involve any moving mechanical parts and generates the plug-like velocity profile [1] [2] [3]. Two-fluid flow in microchannel is used as micro-pump [4] [5] [6], switching technique [7] [8] [9], mixing [10] [11] [12] and so on. Models of stratified flow are needed for predicting the flow characteristics, such as pressure drop and in-situ liquid fraction, and are often used as a starting point in modeling flow patterns transitions. "
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    ABSTRACT: This study is motivated by the need to develop a semi analytical model for predicting the stratified two-fluidćflow with a curved interface in a rectangular microchannel under the combined effect of pressure and electroosmosis.ćWith the non-slip boundary conditions at the wall and the matching condition at the curved interface, the fully developedćNavier-Stokes equation and Poisson-Boltzmann equation are solved using separate variable method. Part of parameters inćthe distributions of velocity and electric potential is calculated using the least-square method. Details of the analyticalćtreatment of the two-fluid flow with curved interface are presented. The results show that the analysis can be employed forćconcave, convex and planar interface. The validity of the two-fluid model with curved interface is evaluated by comparingćits prediction with available numerical data and with the results of exact analytical solutions for laminar flows with planarćinterface, comparison of the electric potential distribution and velocity distributions shows excellent agreement with dataćin the literature. Finally, the effects of interface shape on the electric potential distribution, electroosmotic velocityćdistribution, and flow rates are discussed, the results show that the interface shape influences the two-fluid flow inćmicrochannel significantly.
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    • "Consequently, and as correctly first pointed out by Baygents and Baldessari (1998), ion diffusion in EKI results in a conditional instability. EHD instability of two (or more) immiscible fluids in microfluidic devices is another subject extensively studied by Li et al. (2007), Ozen et al. (2006), and Zahn and Reddy (2006), among others, and is not discussed here. Another feature of EKI is that it is driven by an electrostatic force in the bulk of the liquid away from charged solid–liquid interfaces (and hence away from the electric double layers). "
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