CHEMICAL ENGINEERING TRANSACTIONS VOL. 43, 2015 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright © 2015, AIDIC Servizi S.r.l., I SBN 978-88-95608-34-1; I SSN 2283-9216 Nanopowder Fluidization and Mixing Under the Effect of Acoustic Fields Paola Ammendola* a , Federica Raganati b , Riccardo Chirone a a Istituto di Ricerche sulla Combustione - CNR, P.le V. Tecchio 80-80125 Naples, Italy b Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli Federico II, P.le V. Tecchio 80-80125 Naples, Italy paola.ammendola@irc.cnr.it Gas fluidization is one of the best available techniques to disperse and process large quantities of nanosized powders. Nevertheless, on the basis of their primary particle size and material density, fine powders fall under the Geldart group C (<30 μm) classification, which means that fluidization is expected to be particularly difficult because of cohesive forces existing between particles. In order to overcome these inter-particle forces and achieve a smooth fluidization regime, externally assisted fluidization can be used, thus involving the application of additional forces. Among all the available techniques, sound assisted fluidization has been indicated as one of the best technological option. The present work is focused on the study of the fluidization and mixing of nanoparticles under sound assisted conditions. All the fluidization tests have been performed at ambient temperature and pressure in a laboratory scale sound assisted apparatus. In particular, the first section of this work presents the results about the fluidization behaviour of four different nanopowders (Al2O3, Fe2O3, CuO and ZrO2) in terms of pressure drops, bed expansion and minimum fluidization velocity as affected by acoustic fields of different intensity (125-150 dB) and frequency (50–300 Hz). The fluidization of binary mixtures of two powders (Al2O3, and Fe2O3) is also investigated under the application of different acoustic fields and varying the amount of the two powders. Then the mixing between two different nanopowders (Al2O3/Fe2O3) has been investigated from both a “global/macroscopic” and “local/microscopic” point of view. 1. Introduction Due to their unique properties arising from their very small primary particles size and very large surface area per unit mass, nanoparticles (<100 nm) provide higher contact (Raganati et al., 2014a) and reaction efficiencies (Valverde et al., 2013) than traditional materials, thus finding application in different industrial sectors (Ahangar et al., 2014), such as in the manufacture of cosmetics, foods, plastics, catalysts, energetic, biomaterials, microelectro-mechanical systems (MEMS) and adsorption on fine solid sorbents in the framework of CO2 capture technologies (Raganati et al., 2014b). Before processing of such materials can take place nanoparticles have to be well dispersed. In this respect, gas fluidization is one of the most effective available techniques in ensuring continuous powder handling (Alfe et al., 2015), chiefly because of the large gas–solid contact area (Raganati et al., 2014c). Nevertheless, on the basis of their primary particle size and material density, nanosized powders fall under the Geldart group C (<30 μm) classification, which means that their fluidization is expected to be particularly difficult (i.e. characterized by plug formation, channeling and agglomeration) because of cohesive forces (such as van der Waals, electrostatic and moisture induced surface tension forces) existing between particles and becoming more and more prominent as the particle size decreases. Despite of their Geldart classification, nanoparticles can be smoothly fluidized for an extended window of gas velocities, thus implying that primary particle size/density are not representative parameters for predicting their fluidization behaviour. Indeed, due to the interparticle forces mentioned above, nanoparticles are always found to be in the form of large-sized porous aggregates (Shabanian et al., 2012), rather than as DOI: 10.3303/CET1543130 Please cite this article as: Ammendola P., Raganati F., Chirone R., 2015, Nanopowder fluidization and mixing under the effect of acoustic fields, Chemical Engineering Transactions, 43, 775-780 DOI: 10.3303/CET1543130 775