Study On Fluidization Characteristics Of Fine Particles In A Sound-assisted Fluidized Bed

The fluidized techniques of fine particles are gaining increasing importance along with the great application of fine particles to the manufacture industry. But the fluidization of fine particles easily results in channeling and poor fluidized behavior as a consequence of strong particle-to-particle cohesiveness. So various techniques have been proposed to improve the quality of fluidization of fine particles. Especially, the sound-assisted fluidization of fine particles is researched in this work.An experimental apparatus is designed to study the effects of sound wave frequency and sound pressure level on the fluidization of the fine particles. It is essentially composed of a fluidization column, a sound-generation system and a data acquisition set. The fine SiO2 and TiO2 particles have been fluidized in a column 130mm in ID and 1000mm height. The experimental results prove that the quality of fluidization of fine particles is dramatically improved by the application of acoustic field of appropriate SPLs. The minimum fluidization velocity has a minimum value when the frequency of sound waves is 120Hz and it will decrease as the sound pressure level increases. The degree of sound attenuation will increase while bed material is higher and the fluidization quality of fine particles will become poor and the minimum fluidization velocity will increase. Compared with TiO2, the SiO2 fine particles have a better quality of fluidization at the same fluidized conditions.The cluster/subcluster model and oscillators model are used to describe the fluidization characteristics of fine particles in a sound-assisted fluidized bed. The theoretical calculations show that the minimum fluidization velocity umf is decreased with the SPL increased at the same frequency of sound and the quality of fluidization is better. The agglomerations sizes of fine particles in the fluidized bed are smaller under higher SPL. The sound waves have little effect on the agglomerations when it is under 120dB. But the agglomerations sizes will be dramatically reduced to 180μm from 720μm when the SPL is above 130dB. The umf has a minimum value at an appropriate frequency of sound and a good quality of fluidization can exist in a greater ranges of frequency of sound when the SPL is higher.The theoretical calculations are accordant with the experimental results and it shows that the theoretical model can successfully describe the influence of the acoustic field on fluidization of the fine particles.