Mathematical modelling of nanopowder production by vapor-phase processes

A mathematical modeling technique based on fundamental principles has been developed to describe various processes occurring during the vapor-phase synthesis of nanopowders. The model solves the three-dimensional turbulent governing equations of overall continuity, momentum, energy, species transport as well as chemical kinetics in a multiphase domain. Local particle size distribution (PSD) is obtained by solving the population balance model. A brief review of the homogeneous nucleation theory is presented and main factors affecting the nucleation rate of metal and ceramic particles are discussed. The rate of particle growth is calculated by vapor condensation, Brownian coagulation or a combination of both, depending on the type of material. A computational fluid dynamics (CFD) code has been used as the framework from which numerical solution is obtained. The quadrature method of moments (QMOM), which allows the direct tracking of the local PSD, is used to numerically solve the population balance. Examples of the application of this approach to vapor-phase nanopowder synthesis processes such as the chemical vapor synthesis (CVS) of aluminum powder and the flame synthesis of silica nanopowder are presented. Comparisons of the model predictions with experimental results in terms of the average particle size and other process parameters have shown reasonable agreements. The effects of the operating conditions such as reaction temperature and carrier gas feed rate on the PSD have been evaluated. The model technique has shown a considerable potential as a tool for design and scale-up purposes.