Experimental Analysis of Fluidization of Nano Particles

An experimental study was conducted to investigate the structure and behavior of nano particle agglomerates in the fluidized bed systems. A series of fluidization experiments were performed in a glass column using AerosilŪ R974 and AerosilŪ 200 nano particles. It was observed that silica nano particles fluidize smoothly through formation of agglomerates. No bubbles or dead regions were observed during fluidization. The minimum fluidization velocity was found to be around 0.27 cm/s for AerosilŪ R974 nano particles. Very high bed expansion (up to 8 times the initial bed height) was observed in the fluidization of AerosilŪ R974 hydrophobic nano particles. During the fluidization experiment, samples of nano particle agglomerates were taken from the freeboard of the fluidized bed by an adhesive tape. The agglomerate sizes were measured using an Olympus SZx12 optical microscope. The measured agglomerates sizes were in the range of 1-450 ėm. It was found that the agglomerate size depends on the gas flow rate, fluidization time and height of sampling. The agglomerate sizes decreased by increasing gas flow rate. A decrease in agglomerate size was observed with fluidization time until an equilibrium agglomerate size was achieved. The samples were taken from the higher regions of the bed freeboard had smaller agglomerate size.

The terminal velocities of the agglomerates were calculated for the measured agglomerate sizes with the assumption of a sphericity of 0.7 for the agglomerates. The results showed that 92% of agglomerates have terminal velocities below the superficial gas velocity and can be elutriated from the fluidized bed, indicating that the measured agglomerate sizes are reasonable estimates of the nano particle agglomerates in the fluidized bed.