Numerical study of the hydrodynamic characteristics in an agitated tank with side-entry mixer: The effect of stirrer entry angle

Abstract

The main objective of this work is to study the effect of stirrer entry angle β on the hydrodynamic characteristics in an agitated tank with side-entry mixer (side-entry mixing tank) using the CFD simulation method. For validation purposes, the simulation results were compared with the experimental results. Qualitatively, it was found that there was a similar fluid flow in the simulation and experiment results. The agitated tank system consisted of a 40 cm diameter cylindrical tank and a three-blade marine propeller with 4 cm diameter. The working fluid was water, with a liquid height of 40 cm. The rotational speed varied between 100-400 rpm, with the stirrer entry angle (β) set at 0°, 10° and 15° (right-hand side). The modelling configurations used in the simulation were an RNG Standard k-ε model as a turbulence model, coupled with a Multiple Reference Frame (MRF) for the propeller motion approach method in transient conditions. The results show that simulation configuration MRF-RNG k-ε produced realistic results to describe the hydrodynamic characteristics in the side-entry stirred tank. This is supported by the simulation results, which qualitatively produced similar flow patterns in the simulation and experiment. In the quantitative analysis, at higher rotational speeds the circulation flow formed tended to be pushed further from the impeller discharge, which is supported by the average velocity experimental data. Average velocity in the tank had a tendency to increase as the β increased. The predicted average velocities (in m/s) were 0.0175, 0.0185 and 0.0197 at β 0°, 10° and 15° respectively, at a constant rotational speed (400 rpm). Larger β produced high tangential velocity, leading to a strong circulation flow. Applications of this side-entry mixing tank include those in large scale reactors and storage tanks to maintain the homogeneity of the material inside.