Article pubs.acs.org/IECR
Evaluation of Drag Models for Predicting the Fluidization Behavior of Silver oxide Nanoparticle Agglomerates in a Fluidized Bed Alireza Bahramian,*,† Hadi Ostadi,‡ and Martin Olazar§ †
Department of Chemical Engineering, Hamedan University of Technology, Hamedan, 65155 Iran Department of Chemical Engineering, Amirkabir University of Technology, Tehran, 15875-4413 Iran § Department of Chemical Engineering, University of the Basque Country, Bilbao 644, 48080 Spain ‡
S Supporting Information *
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. geneous bubbling fluidization was observed for dense nanoparticles at high gas velocities.19 The distinctive features of a fluidized bed, such as bubbles and pressure fluctuations, are sensitive to bed operating conditions, and as such, they serve as excellent tools for comparing process conditions and evaluating model parameters. Until recently, only point measurements and a statistically low number of bubbles have been used for validation studies because of limitations on experimental techniques for capturing and analyzing the bubbles. Because of this lack of experimental data, average bubble properties and pressure drop measurements have been used for validation purposes. Computational fluid dynamics (CFD) is an effective tool for understanding the hydrodynamic characteristics of gas−solid flows in fluidized beds.20−28 Both the Eulerian−Eulerian two-fluid model (TFM) and the Eulerian−Lagrangian discrete particle model (DPM) are used to study the effects of particle−particle and gas− particle interactions on the hydrodynamics of fluidized beds containing particles with a size from Geldart group A to group D.29 However, most models focus on Geldart B and D particles in bubbling fluidized beds.30−32 In certain cases, the Eulerian approach has been found to be inaccurate for predicting the hydrodynamics of Geldart A particles in bubbling fluidized beds.32 Thus, Ding and Gidaspow used this approach to simulate the formation, growth, and bursting of bubbles using Geldart group B particles in a jet bubbling fluidized bed, and their results are consistent with the experimental ones.33 van Wachem and Sasic investigated the bubble behavior of Geldart
1. INTRODUCTION Industrial interest in the production of submicrometer and nanometric particles is increasing mainly because of their high specific surface areas, which makes them attractive for numerous applications including pharmaceuticals, chemicals, paints, dyes, and ceramics.1−8 Recently, ultrafine powders with a uniform size distribution have given rise to advanced materials for the electronic, laser, polymer, and health care industries, as well as wastewater treatment plants.9−12 Fluidization is an interesting technique, given that it allows isothermal conditions and high productivities to be attained when handling powders, because of its high gas−solid contact efficiency. It should be noted that the fluidization of very fine particles could be limited and even hindered by the presence of strong interparticle adhesion forces. Nanoparticles are 3 orders of magnitude smaller than traditional Geldart group C fine powders (
