Simulation Of The Growth Process Of Titania Nanoparticle Synthesized By Flame CVD

Considerable interest lies in the synthesis and the use of nanosized particles for a variety of applications. Commodities such as carbon blacks, pigmentary titania or optical fibers for telecommunications are typical products of industrial aerosol reactors. Particle characteristics like size and size distribution or the morphology mainly influence the final product quality. This emphasizes the need for a tool for optimization of the reactor geometry and the operating parameters.Using the commercial CFD-code FLUENT, the simulation of the growth process of titania nanoparticle synthesized in a flame CVD process for nanoparticles is detailedly performed. Effects of turbulent models of RNG k- ε, RSM, and standard k-w on flame structure have been examined. The calculated results show that RNG k-e turbulence model produces reasonable predictions for the temperature profile and the shape of the flame, and on the base of this turbulence model, the temperature profile and the shape of the flame are calculated with the pseudo-component titania. By using the additional fluid-particle dynamics (Johannessen et al.2000), the growth processes of titania nanoparticle with the effect of dilution caused by radial eddy dispersion in the flame is synthesized, where the process of all precursor molecules converting to free T1O2 "monomer" molecules occurs instantaneously when the gas temperature exceeds a certain given value, and the effects of both the oxidation of TiCl₄ to the profile of the temperature and particles to the fluid are ignored, and the subsequent formation and growth of particles occur by coagulation caused by Brown collisions between particles with the monomers as starting point and leading to a steadily growing average particle size, and the notion of a collision limited growth, even for the monomers, is based on the assumption that dimeric and larger clusters are stable-a plausible assumption due to the extreme supersaturation of the monomers at the time of their formation. Based on those assumptions, the size of particles is simulated. The calculated results show that the dilution caused by radial eddy dispersion in the flame increased the size of primary particles slightly, but still much smaller than experimental results. The effects of flame temperature and the flow rates of fuel, oxygen and precursor on the sizes of primary particles and aggregates are also analyzed. The results indicate a flame of higher temperature more easily leads to spherical particles; the size of particle aggregates becomes bigger with the longer residence time.