Physical modelling of an aluminium degassing operation with rotating impellersa comparative hydrodynamic analysis

A hydrodynamic study of aluminum degassing by the rotating impeller technique was developed through experimental measurements obtained in a water physical model stirred with different impellers and air injection. The purpose of the work was to better understand degassing operation in molten aluminum through the analysis of the hydrodynamics of the system. Particle image velocimetry (PIV) was employed to measure flow patterns and turbulence characteristics of the ladle as a function of process and design variables, such as: a) impeller rotating speed (536 and 800rpm), b) air flow rate (3liters/min and 0l/min), c) geometric design of the different impellers (impeller A made of a solid disc, impeller B with lateral nozzles and an impeller C with notches), where impellers B and C represent commercial designs. Impellers B and C presented similar flow behavior, with radial projection and pumping effect, while impeller A developed different flow patterns. By increasing the angular speed and the complexity of the impeller, stirring and turbulence increased through the entire ladle, while the vortex intensity grew. Gas injection modified the liquid flow patterns reducing the magnitude of the velocity in the liquid, and significantly increasing turbulence in the ladle.