Annular centrifugal extractors (ACES) based on the principle of Taylor-Couette flow, offer potential advantages over the existing conventional process equipment in many of the engineering applications. In the present work, mass transfer coefficient (k(c)a) were measured for three sizes of annular centrifugal extractors, viz. 30, 75 and 250 mm. The flooding characteristics were also determined which give the maximum permissible flow rate of one phase for a given flow rate of another phase and results are presented in the form of dispersion number (N-D). These hydrodynamic and mass transfer characteristics were investigated over a rotor speed range of 8-40 r/s and the annular gap in the range of 2-25 mm. The rotor speed and the gap range translated into power consumption cover the range of 0.4-500kW/m(3). Suitable correlations have been developed for k(c)a and N-D. (c) 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.