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In the course of the search for a flow pattern optimal for culture growth in vortex bioreactors, our experiments discovered striking flow patterns that existing theoretical models cannot explain. Three immiscible liquids fill a vertical open cylindrical container 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 middle liquid (M, sunflower oil) and upper liquid (U, alcoholic glycerin) circulations. With increasing rotation, counterflows develop near both interfaces LM and MU in upper fluids: the liquids move toward (away from) the axis below (above) the interface that seems paradoxical. Then, unusual topological transformations occur again in the middle liquid flow caused by competition between effects of radial friction and centrifugal forces. Near cylinder boundary at interface MU, new reverse circulation zone developed where the radial velocity became zero and then change sign. These counterintuitive results wait for their theoretical explanation and formulation of new contact conditions at the LM and MU interfaces. [ABSTRACT FROM AUTHOR]

The paper reports the results of experimental and numerical studies of vortex motion in an industrial-scale glass bioreactor (volume, 8.5 L; reactor vessel diameter D, 190 mm) filled 50–80%. The model culture medium was a 65% aqueous glycerol solution with the density ρg = 1150 kg/m3 and kinematic viscosity νg = 15 mm2/s. The methods of particle image velocimetry and adaptive track visualization allow one to observe and measure the vortex motion of the culture medium. In this work, the vortex flow investigation was performed in a practical bioreactor at the operation regimes. Our research determines not only the optimal flow structure, but also the optimal activator rotation speed, which is especially important in the opaque biological culture. The main result is that, similar to the case of two rotating immiscible liquids, a strongly swirling jet is formed near the axis, and the entire flow acquires the pattern of a miniature gas–liquid tornado. The aerating gas interacts with the liquid only through the free surface, without any mixing. This intensifies the interphase mass transfer due to the high-speed motion of the aerating gas. [ABSTRACT FROM AUTHOR]