Prediction of Flow Fields in a Dual-Impeller Stirred Vessel

Numerical simulations were connected for the flow field in a baffled tank stirred by a dual Rushton impeller. For this geometry, LDV measurements show a characteristic dependence of the flow patterns upon the position of the impellers. Two advanced modeling approaches were tested. In the first, the vessel was divided info two concentric blocks, coupled by, a sliding grin technique, and simulations were conducted in time-dependent mode. In the second approach, the vessel was modeled as two partially over-lapping I regions, the inner one rotating with the impeller and rite outer one stationary simulations were run in steady-state mode for each of the two regions, while information was iteratively exchanged between them after azimuthally averaging and transforming for the relative motion. A third set of simulations was conducted for comparison purposes by using a more conventional method, in which the impellers were not explicitly simulated, while their effects were modeled by imposing suitable values of velocities and turbulence quantities (derived from single-impeller experiments) at the blade periphery. The first two techniques gave similar predictions and successfully reproduced the dependence of the flow patterns on the position of the impellers. The latter method required far less computational effort On the other hand, the ir,Impeller boundary, conditions technique failed to reproduce rite experimental flow patterns, because of die inadequacy of single-impeller boundary conditions for the present geometr