Characterizing Jetting in an Acoustic Fluidized Bed Using X-Ray Computed Tomography

Abstract

Understanding the jetting phenomena near the gas distributor plate in a fluidized bed is important to gas–solid mixing, heat and mass transfer, and erosion to any bed internals, which can all affect the performance of the bed. Moreover, acoustic vibration in a fluidized bed can be used to enhance the fluidization quality of the particulate matter and influence the jetting behavior. Characterizing the jetting structure using X-ray computed tomography (CT) in a three-dimensional (3D) fluidized bed, with and without acoustic intervention, is the focus of this study. A 10.2 cm ID fluidized bed filled with glass beads and ground walnut shell, with material densities of 2500 kg/m3 and 1440 kg/m3, respectively, and particle sizes ranging between 212 and 600 μm, is used in these experiments. X-ray CT imaging is used to determine local time-average gas holdup. From this information, qualitative and quantitative characteristics of the hydrodynamic structure of the multiphase flow system are determined. Local time-average gas holdup images of the fluidized bed under acoustic intervention at a high superficial gas velocity show that jets produced near the aeration plate merge with other jets at a higher axial position of the bed compared to the no acoustic condition. Acoustic fluidized beds also have a fewer number of active jets than the no acoustic fluidized bed, which allowed for a more homogeneous gas holdup region deep in the bed. Hence, the acoustic presence has a significant effect on the jetting phenomena near the aeration plate in a fluidized bed.

Probe effects on the local gas holdup conditions in a fluidized bed

“…This result may be due to the jetting effect caused by the aeration plate that is still present at h/D = 0.25, and which can be seen inFigures 4 and 5. Jetting in the aeration region was also noted by Drake and Heindel[6] and quantified by Escudero and Heindel[28]. By the time the fluidization gas reaches h/D = 0.75, there is a lot more uniformity within the bed, leading to smaller probe effects.…”

Characterization of multiphase flows integrating X-ray imaging and virtual reality

“…A B C D It is also of note that the average percent error has a roughly sinusoidal profile in the radial direction when the COR is varied. This radial variation in error is due to the phenomenon of jetting, a phenomenon which has been previously studied in this system by Escudero and Heindel (2015). The holes in the aeration plate are arranged with a single hole in the middle, surrounded by four concentric rings of holes.…”

“…There is also a distinct increase in CT intensity between h/D = 0.05 and h/D = 0.10. This is the result of jetting immediately above the aeration plate (Escudero and Heindel, 2015). Similar to the current varied case, the changes in the flow CT caused by changing the exposure should be canceled out by calculating the void fraction.…”