Enhancement of mass transport and separations of species in a electroosmotic flow by distinct oscillatory signals.*

The mass transport driven by an oscillatory electroosmotic flow (OEOF) through a parallel flat plate microchannel connecting two reservoirs with different concentrations of an electro-neutral solute is studied. The OEOF is caused by the simultaneous effect of zeta potentials at its walls with an oscillatory external electric field, analyzing  three different periodic signals. The governing equations are given by the Poisson-Boltzmann equation, the modified Navier-Stokes equations and the mass transport equation of the solute. The non-dimensionalized equations are solved and four dimensionless parameters appear which control the transport of the solute: an angular Reynolds number, the Schmidt and Peclet numbers and the ratio of the microchannel height to the Debye length. The mass transport of the solute depends on the type of the used periodic electrical signal for driving the electroosmotic flow and is numerically determined. It is observed that there are values of the angular Reynolds number where the total mass transport of species is the same, independently of the molecular diffusion coefficient.