Experimental Observations of Meridional Flow Stagnation in a Three-Fluid Vortex

Abstract

In the search for a flow pattern optimal for culture growth in vortex bioreactors, our experiments discovered unusual flow structures that existing theoretical models cannot explain. Three immiscible liquids fill a vertical open cylindrical container of radius R = 47 mm whose sidewall is still while the bottom disk rotates driving a fluid motion. The centrifugal force pushes the lower liquid (L, aqueous glycerol) from the axis to the periphery near the bottom, creating its toroid circulation that in turn drives toroid circulations of the middle liquid (M, sunflower oil) and the upper liquid (U, alcoholic glycerine). With increasing rotation, counterflows develop near interfaces LM and MU: the liquids move towards (away from) the axis below (above) the interface that seems paradoxical. At a small thickness of M, a stagnation zone arises where the axial and radial velocities vanish and the M liquid only rotates. As M thickness decreases, this stagnation zone expands and occupies the entire volume of the middle liquid. These counterintuitive results await their theoretical explanation and formulation of new contact conditions at the LM and MU interfaces.