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

The paper reports an experimental study of the fluidization behaviour of mixtures of two solids differing in size at various average compositions. The segregation phenomena accompanying the onset of the fluidized state are analysed and the relevance of the composition profile of the binary bed to the definition of its minimum fluidization 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 fluidization and for restoring the predictive ability of theoretical equations. To this purpose. Carman-Kozeny equation is rewritten in a differential 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 fluidization of dissimilar solids. The evolution of bed composition profiles from the fixed to the fully fluidized state, where the gas drag Force first balances the particulate bed weight, makes clear that full fluidization 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 fluidization, rather it is the sign of its incompleteness. (C) 2001 Elsevier Science Ltd. All rights reserved.