Entrainment of Nanoparticles in a Fluidized Bed
Nanoparticle handling and processing technologies have received widespread attention because of the increased use of nanoparticles in the manufacture of drugs, cosmetics, foods, plastics, catalysts and advanced materials. Some recent studies have shown that nanoparticles may be fluidized in the form of ‘light’ and ‘loose’ agglomerates. These agglomerates are dynamic in that they are continuously breaking and forming, allowing nanoparticles to move from one agglomerate to another. Therefore, virtually all of the massive surface area of the nanoparticles may be available for contact with gas and hence for reaction in a fluidized bed.
An important phenomenon associated with gas-particle fluidization is particle entrainment from the bed. In most applications of fluidization the carryover of fine particles is considered to be undesirable, whilst in some processes selective removal of some fine particles is advantageous. So far, however, no study of entrainment in a fluidized bed of nanoparticles has been reported in the open literature. In this paper, we present a PIV (particle image velocimetry) study of particle entrainment in a fluidized bed, 46 mm id, in which Degussa Aerosil R974 powder (with a primary particle size of 12 nm) was fluidized. We present size distribution and volume fraction of nanoparticle agglomerates as a function of superficial gas velocity and height above the bed surface. The results are used as a basis for discussion of the mechanisms of nanoparticle entrainment in fluidized beds.