Flame Cvd Synthesis Of Numerical Simulation Of Titanium Dioxide Nanoparticles

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 CVD. 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. With the suppose that the combustion reaction occurs in a single step, the turbulent diffusion flame in the flame CVD process is calculated and the configuration of the turbulent diffusion flame agrees reasonably well with that observed in experiments. To simulate the coagulation and sintering process of nanoparticle in this flame, assumptions are put up as follows: the process of all precursor molecules to free TiO2 "monomer" molecules occurs instantaneously when the gas temperature exceeds a certain given value; the effects of both the oxidation of TiCI4 on the profile of the temperature and the effects of the particle volume fraction on the fluid are negligible. Based on these assumptions, two different particle dynamic models, Kruis'(1993) and Xie's(2002) are respectively implemented into FLUENT to investigate the growth of particles; the results from these two models are compared with each other. It is discovered that the particles/aggregates collision radius calculated from the Kruis' model is perfectly consistent with the sizes of particles from the experiment, but the particle size distribution from the other model is better coincident with the experimental results. With the model by Kruis, the effects of flame temperature and the flow rates of fuel, oxygen and precursor on the sizes of primary particles and aggregates also are analyzed. The results indicate a flame of higher temperature more easily leads to spherical particles; the sizes of particle aggregates become bigger with the longer residence time.