Circulation of an object immersed in a bubbling fluidized bed

Abstract

a b s t r a c tThe motion of a large object in a bubbling fluidized bed was experimentally studied using digital image analysis (DIA). The experiments were performed in a 2 D bubbling fluidized bed with glass spheres as bed material. The object motion was measured using non intrusive tracking techniques, while independent measurements of the dense phase velocity (using Particle Image Velocimetry (PIV)) and bubble velocity (using DIA) were carried out. The effect of the dimensionless gas velocity on the object motion was also analyzed.This work characterizes the circulation patterns of an object with a density similar to that of the bed, but much larger in size. Object size and density remained constant throughout the experiments. A comparison between the motion of sinking objects and the motion of the dense phase provided evidence of the feeble effect of buoyant forces on the motion of sinking objects. In contrast, the motion of rising objects is linked to the motion of bubbles. It was found that objects may be raised to the surface of the bed either by the action of a single bubble (one jump) or by several passing bubbles (multiple jumps). Based on these results, the circulation time of objects throughout the bed is a function of two parameters: the maximum depth attained by an object and the number of jumps during its rising path. This relationship is presented along and the multiple jumps phenomenon is studied in detail. Finally, an estimate of the circulation time of an object based on semi empirical expressions is presented for different dimensionless gas velocities. The probability density function of the circulation time shows two different modes as the object was less prone to be raised at moderate depths. The estimate of the circulation time was found to be in good agreement with our experimental data.

Buoyancy effects on objects moving in a bubbling fluidized bed

“…The distribution of the two last parameters will define the distribution of the circulation times of an object in a BFB. In Soria Verdugo et al (2011), the distributions were obtained for the neutrally buoyant object, N. In this work, the effect of the object character istics and the bed parameters on such distributions is analyzed. Fig.…”

“…The objects were coated with strontium aluminate to emit green light. Further details of the experimental setup can be found in Soria Verdugo et al (2011).…”

“…Object N represented a neutrally buoyant object, but it will behave in a slightly flotsam manner due to its density ratio. This object was analyzed in detail in Soria Verdugo et al (2011) and it is given here as a quasi neutral reference in terms of buoyancy effects. Objects F1 and F2 had densities significantly below that of the bed and showed flotsam behavior.…”

“…In a previous work (Soria Verdugo et al, 2011) the motion of a neutrally buoyant object within a 2 D bed was analyzed. The object was found to describe cycles, moving from the surface of the bed to a certain depth and back to the surface by the action of several passing bubbles, as explained by Rios et al (1986).…”

3D Eulerian modeling of thin rectangular gas–solid fluidized beds: Estimation of the specularity coefficient and its effects on bubbling dynamics and circulation times

“…In a study of solids circulation in a thin rectangular bed (pseudo-2D) using particle image velocimetry and digital image analysis (PIV/DIA), the upward particle velocities were found to be only 0.2 of predicted bubble rise velocities [22]. To date there has been only one study which simultaneously measured the upward solids velocity of particles and bubble velocity.…”