Formation of vortices in a combined pressure-driven electro-osmotic flow through the insulated sharp tips under finite Debye length effects

Formation of vortices in an electro-osmotic flow possesses engineering applications in enhancing and controlling the microfluidic mixing. In this paper, we investigate the combined pressure-driven electro-osmotic flow through the insulated sharp tips in a straight microchannel when a direct current electric field is imposed. Maximum vorticity generated near the tip back is influenced by the local Reynolds number and tip sharpness. Under a finite Debye length, the way to control the recirculation region for the single tip is discussed. Such control is applied to a pair of sharp tips which are designed as the symmetrical and asymmetrical ones in shape, or the ones staggered in position. Poisson–Boltzmann model is solved to simulate the flow by the finite element method. Results are shown to support the assumption of finite Debye length and expected to be helpful in controlling the vorticity and recirculation in the relevant microfluidic devices.