Analysis of the effect of mixing vane geometry on the flow in an annular centrifugal contactor

Abstract

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

Liquid–Liquid Mixing Studies in Annular Centrifugal Contactors Comparing Stationary Mixing Vane Options

“…As demonstrated in previous CFD simulations, [6] the addition of a vane-wall gap leads to a region of high rotating velocity near the housing wall and reduces the vanes' pumping efficiency leading to a higher overall annular liquid height. Thus, in each case there is a high velocity region just outside the vane tip.…”

“…The curved vane geometry of the V05 has uniform full-height vanes which differs from that for the V02 model contactor which has a non-uniform, two-tiered vane height as noted elsewhere. [6] For the V05 contactor, each of the four vane types also had a radial gap of approximately 0.25 in (0.635 cm) between the outer edge of the vane and the inner wall of the housing. For these measurements the aqueous weir diameter for the V05 contactor was 2.55 in (6.45 cm).…”

“…While there are some tools to aid in selection of the heavy phase weir size, [4] little guidance is available on selection of housing vane geometry to optimize unit operation for desired flow conditions-which are themselves typically pre-determined by the desired chemical process outcomes rather than by engineering considerations of the conditions for best hydraulic operation of the device as long as the hydraulic operation is stable and acceptable. Previous two-phase (liquid/gas) experimental [5] and computational studies [6] have explored the impact of the configuration of the stationary housing vanes on the height of the liquid in the annular mixing zone. From this, an expected mixing behavior for different vane configurations can be inferred with vanes (and operational conditions) that produce a higher liquid height yielding a smaller average dispersed phase droplet size and a proportionally longer residence time due to increased hold-up volume.…”

Summary report on liquid-liquid contactor scoping experiments and validation test case definition

“…Unlike the straight vanes packages for the smaller CINC-V2 contactor, all supplied vane types for the larger V5 unit used here have vanes that do not extend all the way to the housing wall. As demonstrated in previous CFD simulations [2], the addition of a vane-wall gap leads to a region of high rotating velocity near the housing wall and reduces the vanes' pumping efficiency leading to a higher overall annular liquid height. Thus, in each case there is a high velocity region just outside the vane.…”

FY12 summary report on liquid-liquid contactor experiments for CFD model validation

“…There are also differences in the curved vane geometry between the two scales; while both have a gap between the vane edge and the wall (approximately half the annular gap width in both cases), the V5 vanes have a uniform vane height while the V2 vanes have a stepped region with half the height on the outer ∼1/3 of the vane length as described in Wardle et al [2]. This results in a slightly higher liquid height (in relative terms) in the V2 (with the stepped vane height) as compared to the V5 due to a decrease in the pumping efficiency of the vanes.…”