Prediction of complete mixing of liquid-fluidized binary solid particles

Abstract

In a liquid-fluidized bed consisting of density- and size-different binary solid particles with a given bulk composition, complete mixing may be observed at a liquid velocity less than the terminal velocities of the constituent particles. In such cases a change either in liquid velocity or in bulk composition results in stratification of the bed. A theoretical model to predict relationships between the bulk composition and the critical velocity for complete mixing is developed on the basis of momentum equations for each particle component. The voidage function involved in the equations is independently given from a unit cell model with assumptions of creeping flow around the particle within the fictitious spherical cell and of a potential flow outside the cell. Although the voidage function estimates monocomponent bed expansions to an accuracy comparable to that of the empirical Richardson-Zaki equation, it is not accurate enough when used for predicting the volume fractions of binary particles at complete mixing. The prediction is highly sensitive to monocomponent bed-expansion characteristics, and closer agreements between the predicted and observed results are obtained when experimental expansion data are used in the prediction. Nonetheless, the present model gives correct predictions for totally segregating particle systems. Thus, a segregation map is then illustrated which predicts the mixing state of any given binary particle system and is well comparable with the observed results not only from the present work but also from other existing investigations.