Residence time distribution and flow patterns in the single-phase annular region of annular centrifugal extractor

Abstract

Flow between two concentric cylinders with high-speed rotation of the inner cylinder, also termed as turbulent Taylor-Couette flow, is an integral part of annular centrifugal extractor (ACE). The vortex motion in the annular region causes intense mixing, of the two liquids, and their separation occurs in the inner cylinder under centrifugal action. In the present work, a systematic study of residence time distribution (RTD) in the annular region of ACE has been carried out experimentally as well as using computational fluid dynamics (CFD). The effects of rotational speed (10 ≤ ω ≤ 40, r/s), aspect ratio of annulus (11 ≤ Γ ≤ 48), width of annular gap (1.5 ≤ d ≤ 6.5, mm), and the flow ratio of the immiscible fluids (0.73 ≤ FR ≤ 2.4) have been systematically investigated. Effect of flow ratio, annular gap, and rotational speed has been investigated on the RTD. It was found that the flow in ACE is near to back-mixed behavior because of the presence of counterrotating vortices. The number of vortices depends on the rotational speed and the geometrical parameters of ACE. An attempt has been made to reduce back-mixing by providing radial baffles in the annulus. Good agreement was observed between the experimental measurements and CFD predictions of RTD.