Effect of elasticity on the induced charge electro-osmotic mixing of viscoelastic fluids in a micromixer with a conductive cylinder

Mixing of reagents in microfluidics is critical, and currently, the focus is on Newtonian fluids, but these reagents are often viscoelastic fluids. In this study, a micromixer containing a conductive cylinder is proposed based on the principle of induced charge electro-osmosis (ICEO). The Oldroyd-B constitutive model was chosen to characterize the flow properties of viscoelastic fluids, and the Poisson–Boltzmann model was used to describe the ion distribution in the electrolyte. The impact of the elasticity number (El) of viscoelastic fluids on the mixing efficiency, velocity, and vortex in the micromixer was studied. The results show that the mixing efficiency is only 55.41% when El = 0 (Newtonian fluid), and the mixing efficiency reaches 99.08% when El = 50. As El increases from 0 to 50, the cross-sectional average velocity at 50 μm from the micromixer exit decreases from 160 to 26.1 μm/s. Furthermore, the vortices around the conductive plate generated by the ICEO phenomenon begin to fluctuate at El = 7.