Three-Dimensional CFD-Population Balance Simulation of a Chemical Vapor Synthesis Reactor for Aluminum Nanopowder: Nucle
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BECAUSE of its capability to react with oxygen and produce environmentally benign energy, hydrogen is a promising alternative energy source. Some identified materials with high potential of hydrogen storage are NaAlH4,[1] LiAlH4,[2] Mg(AlH4)2,[3] and AlH3,[4] which have aluminum as an important starting reactant. Nanocrystalline materials represent a powerful tool to make vast improvements in the hydrogenation kinetics of these materials. As mentioned in our previous work,[5] one method for obtaining powders with small particle sizes is the chemical vapor synthesis (CVS) process. This method also offers the ability to produce powders of many different compositions, homogeneity of powder composition, and ease of dopant. In recent years, aluminum nanopowder has been prepared successfully by the CVS process.[6,7] The use of computational models to simulate nanopowder synthesis reactors[8,9] as an engineering design tool is gaining importance because of the increased availability of faster computers. Based on the integration of the principles of transport phenomena and chemical reaction kinetics, computational fluid dynamics (CFD) simulation can be used for determining the optimum reactor configurations and operating conditions.[5,10–12] S.E. PEREZ-FONTES, Graduate Student, and H.Y. SOHN, Professor, are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112. Contact e-mail: [email protected] Manuscript submitted March 21, 2011. Article published online November 9, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
Several researchers have worked on the modeling of synthesis processes of ultrafine aluminum particles and other materials such as silicon. Panda and Pratsinis[13] developed a simplified plug-flow model for an aerosol flow reactor operating at nonisothermal conditions. A carrier gas saturated with aluminum vapor was flowed into a horizontal tubular reactor. As the gas mixture cooled down, particle formation and growth took place. The proposed model includes particle nucleation, condensation, and coagulation. In this approach, the authors assumed a monodispersed particle size distribution. Their results agreed qualitatively with the available experimental data. Schefflan et al.[14] proposed a model for a laboratory-scale tubular reactor in which a plug of aluminum is heated with microwave energy to produce aluminum gas that is carried by helium. The model solves the general dynamic equation (GDE) through a sectional method with particle volume and reactor holding time as the independent variables. The authors reported on the changes in particle size distribution with the residence time as a parameter. Prakash et al.[15] described a simple numerical method to solve the GDE based on a sectional approach in which the particle size distribution domain is discretized into finite-sized sections. The model involves nucleation, surface growth, and coagulation. Computed results were shown for the synthesis of aluminum particles in an aerosol flow reactor. Setyawan and Yuwana[12] presented a
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