Annular centrifugal extractors (ACE), based on the principle of Taylor-Couette flow, offer potential advantages over the existing conventional extraction equipments in many of the engineering applications. In the present work, dispersed phase hold-up (is an element of(D)) and effective interfacial area ((a) under bar) have been measured in 30, 75 and 250 mm rotor diameter annular centrifugal extractors over a wide range of power consumption (0.4 < P/V < 500, kW/m(3)) and physical properties (900 < rho(C) < 1300, kg/m(3); 600 < rho(D) < 1600, kg/m(3); 0.84 < mu(C) < 10, mPa s; 0.6 < mu(D) < 27, mPa s; and 2.2 < sigma < 58, mN/m). From these measurements, Sauter mean drop diameter (d(3,2)) has been estimated. Suitable correlations have been proposed for is an element of(D), (a) under bar, and d(3,2), which are expected to be useful for practicing engineers. Power consumption was also measured for 40, 60 and 100 mm, diameter rotors and an appropriate and simple correlation for power number for ACE has been proposed. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.