Minimum fluidization velocity (Umf) of three ultrafine particles (SiO2

Al2O3 and TiO2) was measured in a fluidized bed with inner diameter of 50 mm. The primary particle size (dp) of these ultrafine particles was ranged from 30 nm to 5 μm and Geldart A reference particle was a size of 45 μm. Results show that all three particles have the same Umf change pattern with increase of primary particle size. Umf first increased gradually as dp increased from 30 nm to 5 μm and then Umf decreased sharply as dp increased further to 45 μm. Umf at dp=45 μm was close to that of dp=30 nm and 200 nm. Umf of different materials decreased in the order of TiO2

Al2O3

SiO2. For particles of the same material

dp effect on Umf was similar to that of repose angle

which reached to a maximum at dp=5 μm. Simulation by agglomerate force balance model shows that average size of fluidized agglomerates is changed similarly to that of Umf with regards to different materials and primary particle sizes.