THE CONCENTRATION PROFILE OF A TWO COMPONENT BED AFTER DEFLUIDIZATION: the phase equilibrium analogy

When gradually and slowly defluidized from the condition of full suspension, any two solid mixture gives place to a fixed bed with a characteristic and repeatable axial composition profile. As it is the result of the spontaneous tendency of the two particulate components to assume a peculiar equilibrium configuration at any velocity between the final and the initial fluidization threshold, such a composition profile illustrates the tendency of the mixture to assume a mixed or a segregated state in the fluidized condition. A certain analogy exists between the process of fluidization/defluidization of a two-solid bed and the liquid-vapor transition of a binary mixture, so that the point of final fluidization can be regarded as the analogous of the dew point of the liquid-vapor equilibrium. On this basis, it is shown that the final fluidization velocity and the concentration profiles of the bed after defluidization are closely related, as they can be determined by means the same equilibrium equation. The model on which the analysis is based is supported by a series of experiments carried out on two binary mixtures of solids, whose diversity of behavior is mainly a consequence of the different density ratio of their components.