For many processes in chemical industry or biotechnology the homogeneous distribution of solids and gases in a continuous liquid phase is necessary (e.g. heterogeneous catalysis or immobilization of microorganisms). For this application Jet-Loop Reactors are widely used to ensure a homogeneous suspension with low power inputs. A major obstacle in the design of Jet-Loop Reactors in three phase flow operation is the calculation of the power demand, gas- and solids hold-up and loop velocity due to the pressure drop of the suspension. This is usually calculated by momentum balance equations with simplifications such as a constant pressure drop for the liquid phase and no interaction between gas and solid phases (M. Kraume, P. Zehner, Concept for scale-up of solids suspension in stirred tanks, Can. J. Chem. Eng. 80 (2002) 674-680; E. Camarasa, A hydrodynamic model for air-lift reactors, Chem. Eng. Proc. 40 (2001) 121-128; P. Zehner, R. Benfer, Modelling fluid dynamics in multiphase reactors, Chem. Engng. Sci. 51 (10) (1996) 1735-1744; K.H. Tebel, P. Zehner, Fluid dynamic description of Jet-Loop Reactors in multiphase operation, Chem. Eng. Technol. 12 (1989) 274-280) although the influence of solid particles on the behaviour of bubbles is well known (L.-S. Fan, K. Tsuchiya, Bubble wake dynamics in liquids and liquid-solid suspensions, Butterworth-Heinemann, Boston, London, Singapore, Sydney, Toronto, 1990.). Local and overall measurements in a Jet-Loop Reactor in three-phase operation have shown significant discrepancies between calculated and measured data (S. John, H. Parchmann, M. Schlueter, N. Raebiger, Effect of particles in bubble wakes on hy-drodynamics in three-phase flows, ASME Fluids Engineering Division Summer Meeting, FEDSM2003-55221, 2003A; S. John, M. Schluter, N. Rabiger, Effect of particles in bubble wakes on hydrodynamics in three-phase flows, FEDSM2003-55221, ASME/JSME Joint Fluids Engineering Division Summer Meeting, Honolulu, 2003B). Now recently developed measurement techniques provide us with a deeper insight into local effects in three-phase flows and their influence on pressure drop and hydrodynamics (S. John, S. Scheid, H. Parchmann, O. Bork, M. Schluter, N. Rabiger, Model fundamentals for the design of three-phase loop reactors, J. Heat and Mass Transf. (2004)), and enable a better modeling and model validation. (c) 2004 Elsevier B.V. All rights reserved.