A major problem of hybrid modelling is the selection of the most realistic structural flow model to represent a reactor equipment unit. Based on CFD simulation, the paper is considering the best version of a circulation flow model for description of the flow pattern in bubble columns. The 3D Euler-Euler model of two-phase flow is solved to prepare the fundamental instantaneous mixing images of bubble column. Two cases of different viscosity including water and aqueous solution of saccharose and gas bubbles at two different diameters to mimic bimodal extremes have been visualized. The model validity is confirmed by comparison with instantaneous gas hold-up experimental data measured by conductometry. More than 100 flow images were examined and compared with four reference bubble-bed structural models. The unsteady flow structures occurring naturally in the bubble column were identified. The frequencies of the vertical structures were of the order 10(-1)-10(0) Hz. The structure composed of a macro vortex with large single loops was found to appear alternatively in crossed planes; accordingly, the multiple cell cross-flow circulation suggested earlier by Zehner has been found as the most appropriate. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.