Evaluation of Drag Models for Predicting the Fluidization Behavior of Silver oxide Nanoparticle Agglomerates in a Fluidized Bed

Abstract

The fluidization characteristics of nanoparticle agglomerates have been experimentally and numerically studied in a fluidized bed. The experimental studies were carried out in a bed containing silver oxide dry powder belonging to group B of Geldart's classification with a primary particle size of 30 nm. Pressure drop measurements using an optical fiber technique allowed the effects of particle loading and inlet gas velocity on the fluidization characteristics of the particles to be determined. Interparticle adhesion forces between silver oxide nanoparticles give rise to the formation of agglomerates with a wide size distribution. Furthermore, a considerable number of bubbles are formed in the bed with agglomerate bubbling fluidization and low bed expansion. Numerical simulations were also performed to evaluate the sensitivity of gas−solid drag models. An Eulerian multiphase model was used with different drag models. A mean particle size of 175 μm was chosen for the numerical simulations, and the results obtained for the minimum fluidization velocity and bed expansion ratio show that the modified Syamlal−O'Brien model provides the closest fit to the experimental data.

Numerical and Experimental Analysis on the Hydrodynamic Behaviors of Nanoparticle Agglomerates at Moderate Reynolds Numbers

“…Because of their unique properties, nanoparticles (NPs) have attracted much attention during the past decade. High surface-to-volume ratios and exclusive physical, chemical, optical, and electromagnetic properties have made them applicable in different industries such as catalysts, biomaterials, medicines, plastics, and so forth. , As interparticle attractive forces are several orders of magnitude larger than the particle weight, NPs always exist in the form of agglomerates but not individual particles. , The hydrodynamic behaviors of agglomerates and the detailed flow characteristics of the scales smaller than the agglomerates play an important role in several practical situations, such as the fluidization process of agglomerates in the fluidized bed reactors. However, information about such hydrodynamic behaviors is still limited, attributed to the complex hydrodynamic conditions of the fluidized bed and the fragile structure of agglomerates.…”

An adhesive CFD‐DEM model for simulating nanoparticle agglomerate fluidization

“…In literature, there are a few studies trying to model nanoparticle fluidization by assuming complex agglomerates as particle (Bahramian et al, 2013;Wang et al, 2008). By treating the simple agglomerate as the DEM particle, one advantage is that we do not need to model particle fragmentation.…”

Structure and Drag Characteristics of Fluidized Nanoparticle Agglomerates at the Bottom of the Bed

“…Some empirical or semiempirical theories were proposed to relate the density of FNPAs with the bulk density of nanopowders. ,, Some investigators also combined the Richardson–Zaki law and fractal theory to predict the average density of FNPAs in the bed. ,, Wang et al and de Martín et al measured the terminal velocity and size of midupper FNPAs in their settling processes by optical methods and they calculated the density of each FNPA under the balance of buoyant weight and drag force. Due to the lack of a drag model suitable for FNPAs, the drag force of each FNPA was calculated by the drag coefficient of its equivalent solid sphere rather than its actual value. , Some simulated and experimental studies on the porous sphere show that the drag behavior of a porous sphere may be different from that of a solid sphere. − Thus, the above method may bring in a deviation of the calculated drag force and then the weight and density. Besides, the hierarchical structures of midupper FNPAs have been revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations by Yao et al Fabre et al and de Martín et al further explained the formation process of this structure feature by neutron scattering and image analysis; they claimed that primary NPs link to form aggregates during production, then aggregates form simple agglomerates during storage, and then simple agglomerates form FNPAs during fluidization.…”