Annular centrifugal extractors (ACEs) based on Taylor-Couette flow, have found various applications, some of which include liquid-liquid extraction and as bio and polymerization reactors. The residence time distribution (RTD) was measured in three size extractors having 50, 150 and 250 mm rotor diameter. The rotational speed was varied in the range of 10-30 r/s so that the power consumption per unit mass in the annular region was in the range of 25-750 W/kg. The extent of axial mixing was substantially reduced by providing helical baffles in the annular region. The effect of pitch was also studied. All the geometries were simulated using computational fluid dynamics (CFDs). A good agreement was obtained between the CFD predictions and the experimental measurements. Also, correlations have been proposed for Peclet numbers in the absence and presence of helical baffles. (C) 2012 Elsevier B.V. All rights reserved.