A fundamental approach to the phenomenology of fluidization of size segregating binary mixtures of solids

The paper reports an experimental study of the #uidization behaviour of mixtures of two solids di!ering in size at various average compositions. The segregation phenomena accompanying the onset of the #uidized state are analysed and the relevance of the composition pro"le of the binary bed to the de"nition of its minimum #uidization velocity is discussed. It is demonstrated that the recognition of the dependence of bed voidage and particle average diameter on mixture composition is the essential condition for getting over current empirical approaches to segregating #uidization and for restoring the predictive ability of theoretical equations. To this purpose, Carman}Kozeny equation is rewritten in a di!erential form suitable for the peculiar characteristics of two-component systems. The good agreement with experimental data indicates that the extension of the fundamental approach from monodisperse to binary beds greatly reduces the number of independent variables to be dealt with in the study of segregating #uidization of dissimilar solids. The evolution of bed composition pro"les from the "xed to the fully #uidized state, where the gas drag force "rst balances the particulate bed weight, makes clear that full #uidization is constantly associated to the achievement of practically thorough mixing. It can therefore be assumed that component segregation is not a distinctive property of binary fuidization, rather it is the sign of its incompleteness