Acoustic Field Effects on Minimum Fluidization Velocity in a 3D Fluidized Bed

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 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.

Characterization of the hydrodynamic structure of a 3D acoustic fluidized bed

“…Similar results were found by Escudero and Heindel (Escudero and Heindel, 2012) using glass bead particles.…”

Characterizing Acoustic Fluidized Bed Hydrodynamics Using X-Ray Computed Tomography

“…As shown in Figure 3, x-and y-slice images at every HID ratio shows multiple air jets that are caused by the aeration holes of the distributor plate. More jetting can be observed in the images without the presence of an acoustic field, this phenomenon is attributed to the fact that the volume of air that is passing through the bed material is slightly higher than the flow rate that is passing through the bed with acoustic field presence because the minimum fluidization velocities are slightly different [13].…”

“…As hiD increases (moving higher in the bed), gas holdup remains fairly constant for both cases; however, the acoustic condition shows a more uniform gas holdup distribution throughout the entire bed, which was also observed in the qualitative images (Figure 3 and 4). Near the top of the bed (hiD ~ I), the no acoustic condition has a higher bed expansion due to a slightly higher gas flow rate [13], which causes more material to be expelled from the bed. Similar trends as the ones shown in Figure 5 are observed when the superficial gas velocity changes.…”

“…X-ray computed tomography (CT) scans are captured with and without acoustic intervention at different HID ratios (0.5, 1, 1.5) and different superficial gas velocities U 8 = 1.5 and 3 U 111 r, where U 111 r is the minimum fluidization velocity previously determined [13].…”

Experimental analysis and computational fluid dynamics simulations for heat transfer in sound assisted fluidized bed of fine powders

“…The investigations for heat transfer for different sized particles at different acoustic conditions, gas velocities, and angular positions around the circumference of heat transfer surface were carried out [17]. The optimum fluidization velocities and acoustic conditions for better heat transfer rates from the surface to the bed material were found out.…”