Electrohydrodynamic instabilities in microchannels: A computational study

A computational study is performed to study mixing characteristics in electrohydrodynamic flows at length scales of a micro-metre. A t-shaped microchannel is analyzed where two fluids of differing electrical conductivities are allowed to mix under the application of an external electric field. A two dimensional finite volume code based on the SIMPLE algorithm is employed. The effect of mixing is characterized in terms of a nondimensional parameter lambda measuring the relative magnitude of the Coulombic force due to the electric field to the inertia force. Based on the relative concentrations of the two mixing streams a mixing efficiency is proposed and the mixing characteristics are studied by varying the value of the parameter lambda (while keeping the concentration ratio fixed). Some observations regarding the time period of oscillation of the disturbance in the absence of any forcing are reported. Simulations are also performed by oscillating the applied external electric field to see the effect it has on the mixing compared to the case with the d.c. electric field. It was observed that oscillation of the electric field at the natural frequency significantly enhances the mixing quite in agreement with the general character of experimental observations. Simulation results for these different cases are presented.