A physical model is presented which descri'bes the local mixing in the liquid phase of twophase gas-liquid flows agitated by rising bubbles. It corresponds to the stochastic mathematical model descrii by Nassar et al (1992). The transport of liquid in the bubble wakes is assumed to be the dominating mixing mechanism. Experiments on single bubbles have been performed in order to demonstrate the key aspects and to estimate the characteristic parameters_ It could be shown that the model can describe the local mixing behavior of the two-phase flow within the riser of an airlift loop reactor at different superficial gas velocities. KEYWORDS Local mixing two-phase gas-liquid flows, bubble wake mechanism INTRODUCHON Mixing in the liquid phase flow of bubble driven multiphase reactors like bubble columns anie;fz loop reactors is not completely . Most scientific contributions discuss mixing on the reactOr scale. In nearly all papers, it is regarded in terms of the axial dispersion model. This model lumps all information about mixing into a single characteristic parameter, the axial dispersion coefficient D . Many attempts can be found in the literaturgto develop a physical meaning for D . Convincing solutions, however, do not exist. # straightforward way of approaching the problem is to look behind the details of the multiphase flows. One such approach was to assume that local mixing mechanisms which apply to the flows in single phase systems also apply to the multiphase flows For example, Baird . and Rice (1975) assumed the local isotropic turbulence theory to be valid and