The Role of Interparticle Force in Nanoparticle Fluidization
Fluidization characteristics of Degussa Aerosil R974 powder having a primary particle size of 12 nm were investigated. The particles were fluidized in a glass vessel of about 50 mm id and 900 mm height using nitrogen as fluidizing gas. The bed was found to rise as a plug owing to strong cohesive force between the particles. After the plug was broken, homogeneous fluidization was achieved as the gas velocity was increased beyond minimum fluidization velocity. The bed was observed to expand uniformly over a wide range of superficial gas velocities, yielding an expansion ratio of up to around 4. However, the characteristics of fluidization were found to be sensitive to initialization of the process and the superficial gas velocity at which the plug was allowed to break. The variations observed in fluidization characteristics were discussed in relation to different initial packing conditions. Bed-collapse experiments were also carried out in order to obtain more detailed information concerning the internal structure of the bed. The results are analyzed in relation to the strength of the inter-aggregate interparticle forces (forces between aggregates).