燃烧法合成二氧化钛纳米颗粒的数值模拟

Simulation of titania nanoparticle synthesis in flame

为了解火焰法合成纳米颗粒过程中流体力学和颗粒动力学作用过程,利用CFD商业软件FLUENT模拟了在湍流扩散火焰中合成TiO2纳米颗粒的过程.模型在没有考虑先驱物TiCl4反应的情况下,计算了在燃烧室内的速度场和温度场.假设当气体温度超过一定数值后,所有先驱物分子迅速转化为TiO2单分子;引入Kruis的颗粒动力学模型对产物颗粒直径、比表面积等进行了预测,研究了不同的火焰结构对其性质的影响,并分析其形成原因.结果表明颗粒的烧结特征,即温度是影响一级颗粒及聚集块尺寸的关键因素;火焰温度越高,聚集块中一级颗粒的数目增长得越快,出口处一级颗粒及聚集块的尺寸也就越大.

To probe into the effects of the interaction of fluid mechanics and particle dynamics in the process of flame synthesis, the simulation of titania nanoparticle synthesis in the turbulent diffusion flame was performed by using the commercial CFD-code FLUENT. Without considering the reaction of precursor TiCl4, both flow field and temperature field in the combustion chamber are simulated and analyzed. All the precursor TiCl4 molecules are assumed instantaneously converted into the product TiO2 monomers when the gas temperature is above a certain value. Kruis' model of particle dynamics has been used and implemented into the CFD-code to predict the sizes and specific surface area of primary and aggregate titania particles. The influence of flame structure on the particle growth process has been discussed. The simulation shows that particle sintering process, i.e. flame temperature is a key parameter for sizes of primary and aggregate titania particles. The higher the temperature is, the faster the growth process gets, and the bigger the sizes of primary and aggregate titania particles become.