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Fluidized beds are used in a variety of process industries because they provide uniform temperature distributions, low pressure drops, and high heat/mass rates. Minimum fluidization velocity is an important factor in understanding the hydrodynamic behavior of fluidized beds, and this characteristic may be modified through high frequency (sound) vibrations. The effects caused by sound wave frequency on the minimum fluidization velocity in a 3D fluidized bed are investigated in this study. Experiments are carried out in a 10.2 cm ID cold flow fluidized bed filled with glass beads with material density of 2600 kg/m 3 , and particles sizes ranging between 212-600 μm. In this study, four different bed height-to-diameter ratios are examined: H/D = 0.5, 1, 1.5, and 2. Moreover, the sound frequency of the loudspeaker used as the acoustic source ranges between 50-200 Hz, with a sound pressure level fixed at 110 dB. Results show that the minimum fluidization velocity is influenced by the frequency change. As the frequency increases, the minimum fluidization velocity decreases until a specific frequency is reached, beyond which the minimum fluidization velocity increases. Thus, acoustic fields provide an improvement in the ease of fluidization of these particles. ABSTRACT Fluidized beds are used in a variety of process industries because they provide uniform temperature distributions, low pressure drops, and high heat/mass rates. Minimum fluidization velocity is an important factor in understanding the hydrodynamic behavior of fluidized beds, and this characteristic may be modified through high frequency (sound) vibrations. The effects caused by sound wave frequency on the minimum fluidization velocity in a 3D fluidized bed are investigated in this study. Experiments are carried out in a 10.2 em ID cold flow fluidized bed filled with glass beads with material density of 2600 kg/m 3 , and particles sizes ranging between 212-600 J.lm. In this study, four different bed height-todiameter ratios are examined: HID = 0.5, 1, 1.5, and 2. Moreover, the sound frequency of the loudspeaker used as the acoustic source ranges between 50-200 Hz, with a sound pressure level fixed at 110 dB. Results show that the minimum fluidization velocity is influenced by the frequency change. As the frequency increases, the minimum fluidization velocity decreases until a specific frequency is reached, beyond which the minimum fluidization velocity increases. Thus, acoustic fields provide an improvement in the ease of fluidization of these particles.

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.

Fluidized beds are found in the energy production industry, and knowing their hydrodynamic conditions, such as local gas holdup or volumetric gas fraction, is important for effective operation. Local measurement probes are commonly used to measure local gas holdup. Although the probes are typically as small as possible to mitigate their influence on the local conditions, the invasive nature of this measurement technique has the potential to alter the fluidized bed behavior. This study used a noninvasive measurement technique, X-ray computed tomography (CT) imaging, to determine the local time-average gas holdup everywhere within a 10.2 cm diameter fluidized bed filled with 500-600 m glass beads in which simulated probes were inserted. Three different simulated probe tips (pointed, rounded, and flat) and two different orientations (horizontal and vertical) were investigated at four different bed heights and two different fluidization velocities. The results show increases in local time-average gas holdup when the probes were present, but the scale of the effects was dependent upon the height at which the probes were placed; the lower the probe within the fluidized bed, the larger the local effects. The shape of the probe tip did not show any differences in the local gas holdup. On the

Understanding the jetting phenomena near the gas distributor plate in a fluidized bed is important to gas-solids mixing, heat and mass transfer, and erosion on 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 particulate matter. Characterizing the jetting structure using X-ray computed tomography in a 3D fluidized bed, with and without acoustic intervention, is completed in this study. A 10.2 cm ID fluidized bed filled with glass beads, with material density of 2500 kg/m3 and particles sizes ranging between 212–600 μm, is used in these experiments. X-ray computed tomography (CT) imaging is used to determine local time-average gas holdup. From this information, qualitative 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 into the bed. Hence, the acoustic presence has a significant effect on the jetting phenomena near the distributor plate of the fluidized bed.