Does the Minimum Fluidization Exist?

Abstract

This work proposes an equation giving the pressure drop of a gas flowing through a porous medium or a granular bed. The consequences for the onset of the fluidization are then discussed. It appears that the notion of minimum gas mass-flow rate would improve the description of the transition between fixed and fluidized bed regimes. An equation is then proposed to calculate the minimum fluidization gas mass-flow rate. It is then proved that the minimum fluidization is not only a function of the medium and fluid characteristics but also that it increases with bed inventory. It is then shown that a batch of particles has a minimum fluidization depending on its arrangement in a column and that in some cases, this minimum does not exist at all. As a consequence, the minimum of fluidization, whether it is a velocity or a mass flow rate, cannot be considered as a criterion to characterize a powder.