Electroosmotic mixing of viscoelastic media in a micropillar-laden micro-confinement

Electroosmotic mixer stands as an energy efficient process for mixing biofluids. The present study explores a micropillar-laden microchannel under electroosmotic flow settings to modulate throughput and enhance mixing in viscoelastic medium. Through rigorous numerical simulations solving coupled Poisson–Nernst–Planck and generalized momentum conservation equation for an incompressible viscoelastic fluid modeled using Phan-Thien and Tanner constitutive relation, we report the effect of micropillar configuration, Deborah number (De), Péclet number (Pe), dimensionless Debye length, and surface charge density on the mixing efficiency, scalar dissipation rate, and flow throughput. Our study identifies that the flow vortices induced by virtue of the micropillar geometry play a critical role in mixing and throughput in the system. We observe that the vortices generally appear at thicker electrical double layer (EDL) across all Pe and surface charge densities, while thinner EDL and stronger viscoelasticity suppress these flow structures. In addition, higher Pe induces stronger vortices in thinner EDL. Notably, an increment in the elastic parameters (De and ϵ) results in enhanced net throughput as compared to Newtonian medium, with a non-intuitive mechanism in the context of viscoelastic medium. Mixing quality is reported to be high in configurations delineating stronger vortices. Biofluids generally exhibit thicker EDL and moderate De; thus, the present configuration may prove to be efficient in carrying out mixing of such systems along with reasonable throughput. We envisage that the present study will help to conceptualize the flow actuation and mixing enhancement phenomena in viscoelastic biofluids in micro-confinement comprising patterned micropillars.