Fluidization Behavior Of Nano-particles In Vibrated Fluidized Bed

The behavior of different cohesive nano-particles was investigated in the conventional fluidized bed. It was found that slugs and channels were formed firstly under low superficial gas velocity due to the specific physical and surficial properties of particle. With increasing the superficial gas velocity, slugs and channels vanished, whilst the bubbling in bed was intensified obviously, and there existed a distribution of agglomerate sizes, namely, the agglomerates sizes were small in the upper zone and large in the lower zone. Because of the severe entrainment, the fluidization ability was poor.Vibrations imposed on gas-fluidized beds of nano-particles caused increase in equilibrium pressure drop, and improved fluidization quality obviously with effectively reduction of agglomerate size as well as looser bed layer. At certain amplitude (3mm) of vibrations applied, the minimum fluidization velocity decreased significantly with increasing vibration frequency. Comparing to the fluidization without vibration, the minimum fluidization velocity of SiO₂ under vibration in this study could be reduced by 50%; while the minimum fluidization velocity was nearly independent of vibration amplitude at almost constant frequency of about 40Hz. Experimental results proved that a proper original bed height of nano-particles with a constant bed diameter (40mm) contributed to better fluidization quality which could be obtained at h₀/D=1 for SiO₂ nano-particles. Further, combinations of high gas velocity and low vibration frequency as well as high vibration frequency and low gas velocity assured two domains with favorable conditions to perform stable fluidization. It could be concluded that the effect of fluidization times on fluidization behavior was relatively small comparing with the other three parameters (vibration frequency, amplitude, gas velocity). The agglomerates sizes were relatively stable after the second fluidization.Combining the Ergun and the Richardson-Zaki equations, two types of agglomerate size, namely agglomerate size at the minimum fluidization velocity and agglomerate size at the terminal fluidization velocity, have been calculated to confirm the reduction of agglomerate size. The probability of agglomerate coalescence and breakup has beenanalyzed. The calculated values were in agreement with the experimentalresults.