Simulation of growth of nonspherical silica nanoparticles in a premixed flat flame

The growth of nonspherical silica nanoparticles in a premixed flat flame has been simulated, including the effects of convection, diffusion, thermophoresis, chemical reactions, coagulation, and coalescence. Considering both radiation effect and multistep chemical reactions of methane/air including both oxidation and hydrolysis of SiCl4, combustion analysis in a premixed flat flame was done first to obtain temperature, concentration of gas species, and flow fields. The predicted flame temperatures were in good agreement with the previous experimental data. Two-dimensional aerosol dynamics in which both particle volume and surface area are independent variables was then analyzed to investigate the growth of nonspherical silica particles. Several different models of coalescence of silica particles were studied: viscous flow sintering, atomistic diffusion sintering, fast sintering, and hybrid sintering models. Since the residence time was short and temperatures were not high enough for perfect coalescence of silica particles in the present study, the resulting particles were partially sintered or open-structured aggregates. The variations of total volume/number concentration and diameter of average volume along the flame height were obtained and compared with experimental data. Bi-modal size distributions were obtained at some flame heights.