Miguel Olivas-Martinez

Computational fluid dynamic modeling of the flame spray pyrolysis process for silica nanopowder synthesis

Abstract A computational fluid dynamic model that couples the fluid dynamics with various processes involving precursor droplets and product particles during the flame spray pyrolysis (FSP) synthesis of silica nanopowder from volatile precursors is presented. The synthesis of silica nanopowder from tetraethylorthosilicate and tetramethylorthosilicate in bench- and pilot-scale FSP reactors, with the ultimate purpose of industrial-scale production, was simulated. The transport and evaporation of liquid droplets are simulated from the Lagrangian viewpoint. The quadrature method of moments is used to solve the population balance equation for particles undergoing homogeneous nucleation and Brownian collision. The nucleation rate is computed based on the rates of thermal decomposition and oxidation of the precursor with no adjustable parameters. The computed results show that the model is capable of reproducing the magnitude as well as the variations of the average particle diameter with different experimental conditions using a single value of the collision efficiency factor α for a given reactor size.

A Computational Fluid Dynamic Model for a Novel Flash Ironmaking Process

A computational fluid dynamic model for a novel flash ironmaking process based on the direct gaseous reduction of iron oxide concentrates is presented. The model solves the three-dimensional governing equations including both gas-phase and gas-solid reaction kinetics. The turbulence-chemistry interaction in the gas-phase is modeled by the eddy dissipation concept incorporating chemical kinetics. The particle cloud model is used to track the particle phase in a Lagrangian framework. A nucleation and growth kinetics rate expression is adopted to calculate the reduction rate of magnetite concentrate particles. Benchmark experiments reported in the literature for a nonreacting swirling gas jet and a nonpremixed hydrogen jet flame were simulated for validation. The model predictions showed good agreement with measurements in terms of gas velocity, gas temperature and species concentrations. The relevance of the computational model for the analysis of a bench reactor operation and the design of an industrial-pilot plant is discussed.

Oxidation of Flash Reduced Iron Particles in Various Gas Mixtures Under the Conditions of a Novel Flash Ironmaking Process

A novel flash ironmaking process that directly reduces iron oxide concentrate particles by gas is under development. The goal of this work was to study the possibility of reoxidation of iron particles in various gas mixtures. As the product iron cools down in the lower part of the flash reactor, conditions may become favorable for reoxidation because of equilibrium and high reactivity of iron particles. The effects of temperature (823 – 973 K) and H2O partial pressure (40 – 100 pct., Ptotal = 86.1 kPa) on the reoxidation rate were examined. The pressure dependence was first order with respect to water vapor, and the activation energy was 146 kJ/mol. A complete rate equation that adequately represents the experimental data was developed. For oxidation in O2-N2 mixtures, the effects of temperature (673 – 873 K) and O2 partial pressure (5–21 pct., Ptotal = 86.1 kPa) were determined. Reoxidation in pure CO2 was also investigated at 873 – 1073 K for comparison.

Computational fluid dynamics modelling of nanopowder production by chemical vapour synthesis process

Abstract The chemical vapour synthesis (CVS) process has been applied to the production of nanosized metallic, intermetallic and ceramic particles of 5–200 nm sizes. A multiphase computational fluid dynamics model, which incorporates the gas phase governing equations of overall continuity, momentum, energy and species mass transport in two- and three-dimensional frameworks, has been used as an integral part of the CVS research. The population balance model is coupled with the gas phase equations to describe the formation and growth of nanoparticles. The quadrature method of moments, which allows direct tracking of local particle size distribution, is used to solve the particle population balance. The model has been applied to the CVS of tungsten carbide, aluminium and silica nanopowders from the vapour–phase reactions of precursors. Comparisons of the model predictions with experimental results in terms of average particle size and other process parameters have shown reasonable agreements. The effects of operating conditions, such as reaction temperature and carrier gas feedrate, on the particle size distribution have been evaluated. The model has shown a considerable potential as a tool for designing and scaling up these particle synthesis processes.