An experimental study of solids mixing in a freely bubbling two-dimensional fluidized bed

An experimental study of solids mixing in a freely bubbling two-dimensional bed of 600 to 850 μm glass particles was performed. Vertical and horizontal particle mixing were studied using heated particles as tracers. The steady-state temperature patterns around a heated wire and the transient response to an injected pulse of heated particles were measured. The bubbling behavior of the bed was recorded with a high-speed video camera and an optical bubble probe. Particle motion was found to be closely related to the random bubble motion in the bed. Mixing experiments must, therefore, be repeated numerious times to achieve meaningful results. Vertical particle transport is asymmetrical. Upward displacement is characterized by a mixing length of the order of the bubble diameter, whereas downward displacement is more uniform, and at a much lower velocity level. Horizontal solids mixing is partially due to mixing in the bubble wakes. In a freely bubbling bed, horizontal mixing is considerably augmented by the lateral motion of bubbles.