Effects of acoustic vibration on nano and sub-micron powders fluidization

Fluidization of nano and sub-micron powders with and without acoustic vibration was investigated. The effects of sound pressure level and frequency were studied. Loudspeakers located under the distributor plate were used as the sound source to disintegrate larger agglomerates concentrated at the bottom of the bed. Nanoparticles showed fluid-like behavior similar to Geldart's A group and application of sound vibration improved their fluidization quality. Submicron particles were hard to fluidize and their fluidization quality was partially improved by sound excitation. Bed compaction, caused by rearranging of the agglomerates, was observed for submicron particles at low gas velocities while the bed was fixed. Nanoparticles did not experience any bed compaction. Sound vibration led to a decrease in minimum fluidization velocity and an increase in bed pressure drop and bed expansion for both types of particles. The fluidization quality of both particles increased at low frequencies, while the reverse was observed at higher frequencies. Fluidization of these particles was improved by increasing sound pressure level. There was a critical sound pressure level of 110 dB, below which the effect of sound vibration was insignificant. A novel technique was employed to find the apparent minimum fluidization velocity from pressure drop signals.

Graphical abstractThe effects of acoustic vibration on the fluidization of nano and sub-micron powders were investigated. Acoustic vibration improved the fluidization quality of both particles. Bed compaction, was observed for submicron particles at low gas velocities (fixed bed). Maximum bed expansion occurred at the frequency of 120 Hz which was close to the resonant frequency of the bed particles.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights►Behavior of submicron/nanoparticles under acoustic vibration in fluidized beds. ►Determination of minimum fluidization velocity for submicron/nanoparticles. ►Determination of resonant frequencies of submicron/nanoparticles.