AC two-immiscible-fluid EOF in a microcapillary

Time-periodic aspects of two-liquid flow in a circular microchannel are numerically studied in which electroosmosis and pressure gradient are directly utilized to drive conducting and non-conducting liquids, respectively. The results reveal that hydrodynamic parameters of the two fluids together with the coupling effects between them affect the flow characteristics. Frequency, electrokinetic radius, surface charges at the interface between the two immiscible fluids, viscosity ratio and body force ratio (or equivalently, the ratio of the reference velocities in the pure pressure- and electroosmosis-driven flows) are key parameters which determine primarily important features of the flow. High-frequency flow leads to comparatively small magnitudes of velocity and Poiseuille number; in fact in this case, a finite time is required for momentum to diffuse far into the bulk fluid depending on the angular frequency. In case of higher dynamic viscosity ratio, the flow resistance of the non-conducting fluid is higher, resulting in a steeper velocity gradient at the interface of the conducting liquid. The existence of the interface zeta potential may result in a broader flow field (i.e., higher extrema values). For nonzero body force ratio, a pressure gradient obviously exists in one direction and the periodic flow field is not completely symmetric; hence, a net flow rate in one direction is preferably attained.