A phenomenological (mechanistic) model has been developed for describing the gas and liquid/slurry phase mixing in chum turbulent bubble columns. The gas and liquid phase recirculation rates in the reactor, which are needed as inputs to the mechanistic reactor model are estimated via a sub-model which uses the two-fluid approach in solving the Navier-Stokes equations. This sub-model estimates the effective bubble diameter in the reactor cross-section and provides a consistent basis For the estimation of the volumetric mass transfer coefficients. The strategy for the numerical solution of the sub-model equations is presented along with the simulation results for a few cases. The overall reactor model has been tested against experimental data from radioactive gas tracer experiments conducted at the Alternate Fuels Development Unit (AFDU), La Forte, TX under conditions of methanol synthesis. (C) 2001 Elsevier Science B.V. All rights reserved.