Mass transport in a novel two-fluid Taylor vortex extractor

Flow instabilities occurring in rotating flows can be exploited as a new ap proach to liquid-liquid extraction. Two immiscible liquids are radially str atified by centrifugal force in the annulus between corotating coaxial cyli nders. When the inner cylinder is rotated above a critical speed, Taylor vo r-tices form in one or both of the fluids. Although the flow pattern yields a relatively small amount of interfacial surface area, the surface is high ly active for interphase mass transfer due to the local vortex motion. By a dding countercurrent axial flow, efficient continuous processing is also po ssible. This flow yields a viable extraction process, particularly for flui d pairs that are easily emulsifiable and therefore have limited processing options with the current equipment commercially available. This article dem onstrates that two-fluid Taylor-Couette flow with countercurrent ent axial flow is achievable in practice and explores, experimentally and computation ally, the mass-transfer characteristics of the flow. Experimentally, when t he vortices first appear, axial dispersion decreases and the interphase mas s transfer starts to increase. Upon further increase in differential rotati on rate, the extraction performance continues to improve, with the mass-tra nsfer coefficient proportional to the strength of Taylor vortices. This sug gests that very high extraction efficiencies can be obtained with even larg er relative rotation rates. Furthermore, mass-transfer boundary-layer theor y, in combination with computational fluid dynamics, provides a reliable me thod for predicting the extraction performance.