The motion of particles in a solid-liquid fluidized bed was experimentally studied by video tracking of marked particles in a matched refractive index medium. In this study, two fluidized states are compared, one carefully aligned in the vertical direction ensuring a homogeneous fluidisation and another one with a non-homogeneous fluidisation regime that results from a slight tilt of the fluidisation column of 0.3° with respect to the vertical.
As a result of the misalignment, large recirculation loops develop within the bed in a well-defined spatial region. It is found that in that range of solid fraction (between 0.3 and 0.4), the inhomogeneous motion of the particles leads to significant differences in velocity fluctuations as well as in self-diffusion coefficient of the particles in the vertical direction, whereas the fluidisation height remains unaffected. At lower (less than 0.2) or higher (higher than 0.5) concentration, particle agitation characteristics are almost unchanged in the vertical direction. © 2017 Elsevier Ltd