Article

# Electrohydrodynamic linear stability of two immiscible fluids in channel flow

Electrochimica Acta 04/2006; 51206585(85). DOI:10.1016/j.electacta.2006.02.002

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**ABSTRACT:**Based on a modified-Darcy—Maxwell model, two-dimensional, incompressible and heat transfer flow of two bounded layers, through electrified Maxwell fluids in porous media is performed. The driving force for the instability under an electric field, is an electrostatic force exerted on the free charges accumulated at the dividing interface. Normal mode analysis is considered to study the linear stability of the disturbances layers. The solutions of the linearized equations of motion with the boundary conditions lead to an implicit dispersion relation between the growth rate and wave number. These equations are parameterized by Weber number, Reynolds number, Marangoni number, dimensionless conductivities, and dimensionless electric potentials. The case of long waves interfacial stability has been studied. The stability criteria are performed theoretically in which stability diagrams are obtained. In the limiting cases, some previously published results can be considered as particular cases of our results. It is found that the Reynolds number plays a destabilizing role in the stability criteria, while the damping influence is observed for the increasing of Marangoni number and Maxwell relaxation time.Communications in Theoretical Physics 06/2011; 55(6):1077. · 0.95 Impact Factor -
##### Article: Instability of pressure driven viscous fluid streams in a microchannel under a normal electric field

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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.International Journal of Heat and Mass Transfer 01/2012; 55(23-24):6994-7004. · 2.32 Impact Factor - [show abstract] [hide abstract]

**ABSTRACT:**This report is about microfluidic extraction systems based on droplets of aqueous two-phase system. Mass transfer between continuous phase and dispersed droplet is demonstrated by microextraction of ruthenium red in a microfluidic device. Droplets are generated with electrohydrodynamic method in the same device. By comparing brightness in the digital image of a solution with known concentrations of ruthenium red and those of a droplet in the microextraction, ruthenium red concentration was measured along the microextraction channel, resulting in good agreement with a simple diffusion model. The maximum partition coefficient was 9.58 in the experiment with the 70-mm-long-channel microextractor. The method is usable for terminating microextraction by electrohydrodynamic manipulation of droplet movement direction. Droplets of different ruthenium red concentration, 0.12 and 0.24% (w/w) in this experiment, can be moved to desired place of microfluidic system for further reaction through respectively branched outlets. In this study droplet-based microextraction is demonstrated and the mass transport is numerically analyzed by solving the diffusion-dissolution model.Journal of chromatography. A 06/2010; 1217(24):3723-8. · 4.19 Impact Factor

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