The flows in stage-wise liquid-liquid extraction devices include both phase segregated and dispersed flow regimes. As a additional layer of complexity, for extraction equipment such as the annular centrifugal contactor, free-surface flows also play a critical role in both the mixing and separation regions of the device and cannot be neglected. Traditionally, computional fluid dynamics (CFD) of multiphase systems is regime dependent—different methods are used for segregated and dispersed flows. A hybrid multiphase method based on the combination of an Eulerian multifluid solution framework (per-phase momentum equations) and sharp interface capturing using Volume of Fluid (VOF) on selected phase pairs has been developed using the open-source CFD toolkit OpenFOAM. Demonstration of the solver capability is presented through various examples relevant to liquid-liquid extraction device flows including three-phase, liquid-liquid-air simulations in which a sharp interface is maintained between each liquid and air, but dispersed phase modeling is used for the liquid-liquid interactions.

in Wiley InterScience (www.interscience.wiley.com).The annular centrifugal contactor has been developed as the central piece of equipment for advanced liquid-liquid extraction processes for use in recycling spent nuclear fuel. While a sufficient base of experience exists to support successful operation of current contactor technology, a more complete understanding of the fluid flow within the contactor would enable further advancements in design and operation of future units. In particular, an important characteristic of the flow that is not well understood and which significantly complicates computational modeling of the contactor is the complex free surface flow in the annular mixing zone. This study presents the results of time-dependent, multiphase computational fluid dynamics (CFD) modeling using the volume-of-fluid (VOF) interface tracking method to characterize the mixing zone in a model centrifugal contactor. Laser doppler velocimetry (LDV) measurements of the actual flow velocities within the contactor were also performed. The experimental results were compared with simulations using various turbulence modeling schemes. The CFD model predictions using a coarse grid large eddy simulation (LES) method are in good agreement with the experimental measurements and observations. 2007 American Institute of Chemical Engineers AIChE J, 54: 74-85, 2008

in Wiley InterScience (www.interscience.wiley.com).The annular centrifugal contactor is a compact mixer/centrifuge developed for solvent extraction processes for recycling used nuclear fuel. This research effort couples computational fluid dynamics (CFD) modeling with a variety of experimental observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the volumeof-fluid method combined with large eddy simulation of turbulence was found to have very good agreement with the experimental measurements. A detailed comparative analysis of the flow and mixing with different housing vane geometries (four straight vanes, eight straight vanes, and curved vanes) was performed. Two additional variations on the eight straight vane geometry were also simulated. This analysis determined that at the simulated moderate flow rate the four straight mixing vane geometry has greater mixing and fluid residence time as compared to the other mixing vane configurations. V

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Molecular-dynamics simulations were performed to model the effect of added salt ions on the liquid-liquid interface in a partially miscible system. Simulations of the interface between saturated phases of a model 1-hexanol+water system show a bilayer structure of 1-hexanol molecules at the interface with -OH heads of the first layer directed into the water phase and the opposite orientation for the second layer. The alignment of the polar -OH groups at the interface stabilizes a charge separation of sodium and chloride ions when salt is introduced into the aqueous phase, producing an electrical double layer. Chloride ions aggregate nearer the interface and sodium ions move toward the bulk water phase, consistent with the explanation that the -OH alignment presents a region of partial positive charges to which the hydrated chloride atoms are attracted. Ions near the interface were found to be less solvated than those in the bulk phase. An electric field was also applied to drive ions through the interface. Ions crossing the interface tended to shed water molecules as they entered the hexanol bilayer, leaving a trail of water molecules. Stabilization and facilitated transport of the ion by interactions with the second layer of hexanol molecules appeared to be an important step in the mechanism of sodium ion transport.

This paper presents computational fluid dynamics (CFD) simulations of the flow inside the rotor of an annular centrifugal contactor. The model geometry was based on the rotor of a commercially available contactor unit with a closed upper weir. Simulations were performed at various flow rates and it was found that the narrow flow area above the upper weir seals with water at high flow rates resulting in the formation of a siphon. A method for predicting the zero-point flow rate from CFD was also developed and simulations were performed which demonstrate a zero-point elevation due to this siphon.