Experimental and numerical determination of fluid velocity profiles and turbulence intensity in mixing vessels.

摘要

In this study, both a laser-Doppler velocimeter (LDV) and a computational fluid dynamic (CFD) software package (Fluent) were used to experimentally determine and numerically predict the velocity distribution of an unbaffled and a baffled mixing vessel. Two types of impellers were employed, namely a flat blade turbine (FBT) and a pitched blade turbine (PBT). These impellers were studied in a single-impeller or multiple-impeller configuration in the unbaffled and baffled vessels. The flow characteristics in the impeller regions were measured by LDV and used as boundary conditions in the numerical computation. Turbulence effects were numerically simulated using either the k-;In general, good agreement between the CFD predictions and the LDV measurements was obtained. Predictions in which the boundary conditions were specified at multiple surfaces in the impeller region (i.e., two planes instead of one) were found to be superior to those in which less accurate boundary conditions were used. The predictions based on ASM were typically found to be in closer agreement with the experimental data than those based on the k-;The flow patterns in the unbaffled vessels were found to be dominated by the tangential component of the velocity, regardless the types of impeller used. In the baffled vessels the flow patterns were strongly dominated by the axial and tangential components. The presence of a second impeller in the baffled vessels altered the flow considerably, producing a strong vertical recirculation pattern between the impellers, and significantly reducing the circulation flow below the lower impeller.