Influence of liquid density and viscosity differences on the development of liquid–liquid interfacial area in hydrodynamic focusing

Abstract

The development of the contact surface between mixed liquids and the reduction of striation thickness and filament diameters of the dispersed phase enable effective diffusive transport of components under stable laminar flow conditions. Hydrodynamic focusing accomplishes this at the initial mixing stage by generating viscous stresses tangential to the liquid–liquid interface and normal stresses associated with pressure. As a result, the additive stream forms either an elongated filament (3D focusing) or a thin striation (2D focusing). This work examines the influence of the physical properties of liquids and the focusing method on the intermaterial surface area concentration in vertical flow systems, where gravitational segregation is avoided. The Navier–Stokes equations were solved for the axisymmetric core–ring flow in a pipe and the stratified symmetric flow in rectangular channels of different aspect ratios. The effects of differences in liquid density and viscosity, as well as the axial pressure gradient, on the transverse size of the focused stream and the contact surface concentration were determined for both upward and downward flow. In addition, the influence of the rectangular channel geometry on the residence-time distribution of the additive liquid was analysed.