The concentration profile of two-solid beds after slow defluidization: Model and experiment

Slow defluidization of a two-solid mixture brings to a fixed bed with a characteristic concentration profile of the two species along the bed height, which is related to the initial and the final fluidization velocities of the mixture. The paper shows that the one-parameter model devised for describing the progress of binary fluidization in fundamental terms can be used for calculating the defluidized composition profile. It is discussed how the model equations cover the behaviour of systems that achieve the fluidized condition both through the mechanism of ‘top fluidization’ and that of ‘bottom fluidization’, a condition typical of beds in which the differences in component density and size act simultaneously on the segregation tendency and cause the denser material to be the fluidized component, if sufficiently smaller. Changing the fitting procedure used to assign a value to the parameter of the model is demonstrated to improve its predictive ability, although a limit to it is set from the singularity of the fluid dynamics which characterizes the distributor region at the base of the fluidization column.