Design of a rotor for aluminum degassing assisted by physical and mathematical modeling

Abstract

Recent studies on aluminum degassing [1, 2] show that although the impeller speed and the gas flow rate are important process variables in terms of the productivity and operational costs, the impeller design is also a key design parameter influencing the productivity and the quality of the aluminum in foundry shops. In this work, an improved design of an impeller is tested through a water physical model and mathematical modeling and its performance is compared against commercial designs of impellers. A full-scale water physical model of a batch aluminum degassing unit was used to test the impellers by using the same operating conditions (580 rpm and 40 liters per minute) and by performing deoxidation from water by purging nitrogen into the water saturated with oxygen (similar to the dehydrogenation). A mathematical model based on first principles of mass and momentum conservation equations was developed and solved numerically in the commercial CFD code ANSYS Fluent to describe the hydrodynamics of the system with the objective of explaining the deoxidation kinetics observed in the experiments. It has been found that the new impeller design shows a better performance than the commercial designs in terms of degassing kinetics for the conditions used in this study, which is explained since the new design promotes a flow dynamics that increases the pumping effect, creating a bigger pressure drop and fluid flow patterns which help to drag and distribute more evenly the bubbles in the entire ladle than the commercial designs.