268538 Minimum Fluidization Velocity in a 3D Fluidized Bed Modified with an Acoustic Field

Tuesday, October 30, 2012: 3:55 PM
Conference C (Omni )
David R. Escudero and Theodore J. Heindel, Department of Mechanical Engineering, Iowa State University, Ames, IA

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 either glass beads or ground walnut shell, and particle size ranged between 212-600 microns. In this study, four different bed height-to-diameter ratios are examined: H/D = 0.5, 1, 1.5, and 2. Additionally, the sound frequency of the loudspeaker used as the acoustic source ranged between 50-200 Hz, and the sound pressure level ranged 80-130 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. In the same sense, as sound pressure level increases, the minimum fluidization velocity decreases because the additional acoustic energy imparted to the bed helps to loosen the bed and reduces the required energy for the particles to overcome gravity forces. Thus, acoustic fields provide an improvement in the ease of fluidization of these particles. Our next step is to assess the effects of the acoustic field on the bed flow structures using 3D X-ray computed tomography imaging.

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See more of this Session: Fundamentals of Fluidization III
See more of this Group/Topical: Particle Technology Forum