Advanced statistical analysis of Local Bubble Size Distributions in 2D gas fluidized beds

The principal difficulty in analysing fluidization quality and bubble dynamics is related to the possibility of measuring or predicting the physical and geometrical properties of gas bubbles rising in a granular medium. Even the development of detailed experimental correlations gives poor results, being necessary a fully statistical approach. On the above basis, the present work focuses on the statistical analysis of the behaviour of a 2-D fluidized bed operating under bubbling and slugging conditions, performing measurements of Local Bubble Size Distributions (BSD) along the bed. The analysis allowed to observe a characteristic bimodal shape of BSDs for different particles dimension and fluidization velocities, due to the contemporary presence of random coalescence, splitting and nucleation phenomena. The presence of a characteristic peak of the distribution at small diameters accounts for the enhanced mixing effects due to small bubbles, while the second peak is related to large bubbles responsible for gas by-pass. Conversely, an almost Gaussian distribution is obtained when a BSD weighed on bubble area is computed.