Computational fluid dynamic modeling of chemically reacting gas-particle flows.

摘要

Computational fluid dynamic modeling was performed to describe and analyze the various processes occurring in three chemically reacting gas-particle flows: chemical vapor synthesis of tungsten carbide and aluminum nanopowders, flame synthesis of silica nanopowder, and a novel flash ironmaking process based on the direct gaseous reduction of iron oxide concentrate particles.;The model solves the three-dimensional turbulent governing equations of overall continuity, momentum, energy, and species transport including gas-phase chemical kinetics. For modeling nanopowder synthesis, the particle size distribution is obtained by solving the population balance model. The particle nucleation rate is calculated based on chemical kinetics or homogeneous nucleation theory. The particle growth rate is calculated by vapor condensation, Brownian coagulation or a combination of both, depending on the type of material. The quadrature method of moments is used to numerically solve the population balance. For modeling the flash ironmaking reactor, a simplified chemical reaction mechanism for hydrogen-oxygen combustion is used to calculate realistic flame temperatures. The iron oxide concentrate particles are treated from a Lagrangian viewpoint.;First, the chemical vapor synthesis of tungsten carbide nanopowder was simulated. Using available experimental data, a parametric study was conducted to determine the nucleation and growth rate constants. Second, the flame synthesis of silica nanopowder was simulated. A single value of the collision efficiency factor was sufficient to reproduce the magnitude as well as the variations of the average particle diameter with different experimental conditions. Third, the chemical vapor synthesis of aluminum nanopowder was simulated. Comparison of model predictions with the available experimental data showed good agreement under different operating conditions without the need of adjustable parameters.;For modeling the flash ironmaking reactor, experiments reported in the literature for a nonpremixed hydrogen jet flame were simulated for validation. Model predictions showed good agreement with gas temperature and species concentrations measurements. The model was used to design a nonpremixed hydrogen-oxygen burner. The distributions of velocity, temperature, and species concentrations, and the trajectories of iron oxide concentrate particles in a lab flash reactor were computed and analyzed.