Experimental Study on Fluidization Characteristics of Nanoparticles

Abstract

Recent studies show that nano-sized particles can be fluidized in the form of nanoparticle agglomerates. However, fluidization behavior such as the minimum fluidization velocity and fluidization regime differ significantly for different nanoparticles. Hence this paper is aimed to experimentally investigate the general fluidization characteristics of different nanoparticles. It is interesting to note that a fluidized bed of nanoparticle agglomerates is optically semi-transparent due to the extremely high porosity (typically over 99%) of the bed with respect to the primary materials of nanoparticles. Taking advantage of this unique feature, traditional optical measurement techniques are applied to visualize the flow structure as well as to measure the size of the fluidizing nanoparticle agglomerates. Based on measurements of four different nanoparticle materials, two types of fluidization behavior have been identified, which closely resemble those of classical Geldart Group A and Group B particles, respectively. It shows, however, that the bed of “Group A” nanoparticles expands as long as there is a flow through the bed, which is different from the classical fluidization of Geldart Group A particles where there is no bed expansion until reaching the minimum fluidization velocity. It is also noted that, based on the apparent density and size, the fluidization behavior of nanoparticle agglomerates do not precisely follow the Geldart classification. To differentiate these particles with very similar fluidization characteristics, terms the APF and ABF are introduced for the fluidization classification of nanoparticle agglomerates. Typical fluidization characteristics including bed expansion, bed pressure drop and hysteresis effects of both APF and ABF nanoparticles. The sizes of nanoparticle agglomerates also have been measured using an in-situ optical measurement system.