Linear stability of the interface between a newtonian and a non-newtonian fluid in a microchannel subjected to an electric field

Abstract

Microchannels provide less material use, shorter production and testing times, thanks to their size smaller than 1 millimeter. If two immiscible liquids flow in a microchannel, the interface can be deflected to obtain microdroplets widely used in re actions to achieve better mixing and biological medicine, such as the DNA microarray and cell separation. The aim of this study is to investigate the linear stability of the interface between a Newtonian and a non-Newtonian fluid flowing in a microchannel under the effect of an electric field applied either normal or parallel to the flat inter face. The effects of the electric number, the ratio of the fluid to electric time scales, the Reynolds number, the thickness, the viscosity and the conductivity ratios of the fluids, the base flow strength and the direction of the electric field on the stability are ana lyzed. The results indicate that higher viscosity and conductivity ratios stabilize the system. The stability behavior of the thickness ratio and the Reynolds number depend on the presence or the absence of an electric field. As observed in the Newtonian Newtonian fluids, the electric number can stabilize or destabilize the flow depending on the electrical properties of the fluids. In brief, in the presence of a normal electric field, the stability behavior of the Newtonian-Newtonian and the Newtonian-power-law fluids are qualitatively similar. The stability behavior of the power-law index depends on the thickness ratio and the Reynolds number. The base flow stabilizes the interface for the Newtonian-shear-thinning fluids contrary to the Newtonian-shear-thickening fluids; whereas it does not affect the stability of the Newtonian-Newtonian fluids.