Fluidization of mixtures of two solids differing in density or size

The complex mechanism by which homogeneous mixtures of two solids achieve fluidizationis subjected to theoretical analysis, to elaborate relationships capable to providetheir ‘‘initial’’ and ‘‘final fluidization velocity’’ uif and uff, i.e., the limits thatencompass the suspension process. The article shows how the equation that describesthe force equilibrium of fluidization can be rewritten in forms that account for the distributionof the components of density- or size segregating mixtures during the transitionto the fluidized state. This approach leads to the theoretical expression of uif anduff of either type of system, whose differences of behavior are correctly reproduced byaccounting for the voidage reduction typical of beds of particles of different size. Thecomparison with experimental results at varying mixture composition demonstratesthat the equations give a coherent interpretation of the dependence of the fluidizationvelocity interval of two-solid mixtures on the principal variables of interest.