Practical investigation of mixing phenomena by physical modelling : Scaling criteria applied for bottom gas-stirred water modelling of metallurgical vessels

Sammanfattning: Gas stirring is currently the most commonly used method of homogenizing liquid steel in commercial processes. However, due to the harsh environment during the process, physical models built out of e.g. plexiglass have been used to easier understand the complex phenomenon occurring in the process. The models are also used to optimize stirring conditions and estimate mixing times. Instead of liquid steel, water has been used for modelling, to increase safety and reduce costs. The water models are usually scaled down to sizes that are easier to handle. Scaling correctly requires fulfilling commonly used criteria and dimensionless numbers. This report investigated the accuracy of these dimensionless numbers and the relations commonly used for scaling. Existing studies and relations were evaluated, and the theoretically best suitable scaling equations were tested. Three bottom blown vessels were built, in order to test the existing relations. By applying scaling criteria and calculating gas flow rates accordingly, the correlation between theoretical mixing time and measured mixing time could be investigated. This thesis concluded that the correlation between the measured mixing times was not significant, however, by implementing the scale factor λ1/2 a better approximation seems to be given.