Flow between two concentric cylinders, with either or both of them rotating, has potential advantages over the conventional process equipment. This flow, which is also termed Taylor−Couette flow and exhibits a variety of flow regimes, has been studied using computational fluid dynamics (CFD) simulations. The onset of centrifugal instability, the various cell patterns, and the velocity profiles have been predicted and compared with the available experimental data. To extend the base of experimental information, new measurements have been made using laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). For the entire range of experimental data, the Reynolds stress model (RSM) was determined to exhibit good predictive ability for the mean components of velocity and the turbulent kinetic energy. The wavelengths of the vortices in various regimes have also been determined using CFD and were observed to be in good conformity with all the available experimental results. Furthermore, very good agreement between the predicted energy dissipation rate with the energy input rate was observed over a wide range of speeds and annular gaps.

The single phase flow patterns in the annular region of an annular centrifugal extractor (ACE) have been studied both experimentally and computationally. Experiments were conducted using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) to understand the flow patterns and velocity profiles in both the presence and the absence of the net flow through the annulus. The data obtained in these experiments have been used for the validation of the computational fluid dynamics (CFD) simulations. Further, complete energy balance has been established. The CFD simulations were performed over a wide range of operating conditions. In contrast with the Taylor annular region (having no end effects), the ACE was found to exhibit markedly different cell patterns. The number of cells was found to be strongly dependent on the Taylor number. The effect of the internals such as radial baffles in the annulus, as well as vanes on the bottom plate, on the flow patterns has been investigated. From the simulations it was revealed that the flow patterns in ACE were also dependent on the start-up procedure of the equipment.

Two-fluid Taylor-vortex flow in coaxial cylinders with a stationary outer cylinder and a rotating inner cylinder has potential advantages over the conventional extraction equipment in chemical and bioprocess industries. The two phase flow behavior in the vertical annular region is either in the form of homogeneous dispersion, banded dispersion, segregated or the stratified flow with both the phases retaining individual integrity. Computational fluid dynamics (CFD) simulations have been carried out for the annular region. The effect of physical properties like density difference, interfacial tension, and the effect of geometrical parameters such as annular gap have been studied. The various regime transmissions have been investigated using CFD as well as flow visualization by particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). The flow pattern has also been measured and compared with the CFD predictions. An attempt has been made to present the results on transition in the form of a regime map with the Eotvos and Taylor numbers as the two coordinates.