The minimum fluidization velocity Umf is an important parameter of a fluidized bed. Ramos Caicedo et al. [27] fluidized glass ballotoni (density ρs=2550 kg/m3 particle size dp=250−400 μm) and demonstrated that the minimum fluidization velocity in 2D fluidizedbeds was dependent on the thickness and height of the bed. Thus, significant differences in the Umf (up to 500%) were detected when the bed height was varied from h=8cm to h=60 cm (bed thickness t=6 mm). Ramos Caicedo et al. proposed a correlation for the extrapolation of the Umf in 2D fluidized beds to the Umf of a 3D bed; however, the constant in the proposed correlation was dependent on
the particle size. Thus, the correlation could not be used when different experimental conditions were applied. Moreover, Geldart demonstrated that the minimum fluidization velocity increased with an increase in the fixed bed height; however, only a 43% increased in the Umf was observed when the bed height was increased from 5 to 80 cm. In theory, the minimum fluidization velocity does not depend on the height of the bed; thus, the observed differences in the Umf were attributed to wall effects.