Evaluation of flow patterns in a stirred tank equipped with tubular baffles using CFD numerical models and experimental PIV

Abstract

Stirred tanks are fundamental to the industry, and the geometry of the baffles has a significant impact on energy consumption and flow characteristics. Recently, tubular baffles (TB) have emerged as a promising alternative to reduce energy consumption in these tanks. The integration of numerical simulations with experimental measurements provides a comprehensive understanding of the hydrodynamics in these systems, allowing for a better understanding of the interaction between the baffle and the impeller. This study analyzes the hydrodynamics of agitated tanks with different tubular baffle arrangements using Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV). PIV was used to evaluate different RANS turbulence models and found that the realizable k-epsilon model adequately predicts the flow behavior both near the impeller and in more remote areas where velocities are lower. CFD results show that the geometry of the tubular baffles modifies the flow patterns in the tank, increasing the flow in the lower part and improving the pumping efficiency by 13 % to 20 %. However, the flow analysis shows that the axial flow in the upper part of the tank is low, creating stagnant zones that double the mixing time in the PBT-4 TB case and increase the mixing energy by 76 %. The PBT-8 TB arrangement was found to reduce this difference to 18 % compared to the flat baffle case.