The electrohydrodynamic and shear-stress instability of the interface between two viscous fluids with different electrical properties under constant flowrates in microchannel is analytically and experimentally investigated. In analytical model, the two-layer system is subjected to an electric field normal to the interface between the two fluids; the electric field, surface charge and fluid dynamic are coupled only at the interface. In the experiments, two immiscible fluids, aqueous NaHCO3 (high electrical mobility fluid) and Poly (dimethylsiloxane) (low electrical mobility fluid) are pushed into the PMMA microchannel using syringes and syringe pump. The normal electric field is added to the aqueous NaHCO3 using high voltage power supply; the perturbation electric field are added using a function generator and a power amplifier. The results showed that the electric fields can induce the instability of fluids in microchannel; the increasing of viscosity and flowrates has a stabilizing effect to the flow; but increasing of thickness has a destabilizing effect to the flow. The results also show that the analytical solution has a good agreement with the experimental results.

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