Numerical simulation of hydrodynamics in an uncovered unbaffled stirred tank

Abstract

Numerical simulations were carried out to investigate the turbulent flow with free-surface vortex in an uncovered unbaffled stirred tank. An Eulerian–Eulerian multiphase flow model coupled with a volume-of fluid method was applied to capture the gas–liquid interface and describe the flow field in the tank. Turbulence is computed using a Reynolds stress model with seven equations. The reliability and accuracy of the simulations are verified by comparing the predicted free surface profiles and power numbers with experimental data in the literature. The overall agreements between the simulation results and experimental measurements are obtained. The simulation results show that vortex on the liquid free surface in the uncovered unbaffled tank can be divided into central zone and peripheral zone, and the critical radius of the two zones keeps almost unchanged with enhancing of impeller speeds. At the same impeller speed, vortex becomes deeper and larger with increasing of impeller diameter. However, vortex shape changes not very much with increasing of impeller diameter under the same power consumption. Impeller clearance has no significant influence on the vortex shape. Circumferential flow is dominant in the uncovered unbaffled tank, and the flow field can be divided into forced vortex region and free vortex region. Power numbers in uncovered unbaffled stirred tanks decrease slightly with increasing of the Reynolds number, and are far lower than that in baffled stirred tanks.