Mixing process of immiscible fluids in microchannels

The paper is concerned with experimental investigations and numerical simulations of immiscible flows in microchannels in the presence of interfacial surface tension. The aim of the present study is to model the unsteady dynamics of the vortical structures and interface shape in the Y-branching geometries with square cross-sections. The tested fluids are Newtonian and weakly elastic polyacrylamide solutions in water (modelled as shear thinning Carreau-Yasuda fluids). The experiments used specially designed configurations based on optical and confocal microscopic devices; PIV measurements of the velocity distributions and direct visualizations of the interface are obtained. The simulations performed with the VOF solver implemented in the FLUENT code are validated by experiments for small and medium Reynolds numbers (0.1 < Re < 200). The numerical solutions offer a detailed description of the vortices formation in the vicinity of the interface, phenomena which directly influence the mixing and diffusion processes within the micro-geometry here investigated.