TiO2纳米颗粒在火焰中凝结长大的数值模拟

Simulation of coagulation and growth of titania nanoparticle in flame

颗粒生长的数值模拟是通过流体动力学与颗粒动力学相结合计算实现的。实验表明,温度是颗粒成长中非常重要的因素之一,所以湍流扩散火焰的正确模拟,是颗粒学模型计算结果正确与否的关键。首先在CFD商业软件FLUENT中计算得到准确的丙烷与空气、四氯化钛与空气反应的湍流火焰场;然后应用FLUENT的UDF功能,编制C语言程序引入颗粒学模型进行计算,对颗粒尺寸进行了预测;通过对计算结果的分析探讨火焰温度、氧化剂流量等因素对生成颗粒或者颗粒聚集块尺寸的影响。结果表明:空气流率对火焰场温度影响很大;火焰场温度越高就越容易形成球形颗粒;颗粒在火焰中的时间越长,生成的颗粒或聚集块的尺寸就越大;气体的稀释作用对颗粒成长有一定影响。

The particles dynamics was integrated in the fluid dynamics to simulate the particles＇ growth. The factor for the simulation is the correct turbulent diffusion flame, because the temperature was one of the most important factors in the growth process. The turbulent flame field, C3 H8 with O2 and TiCl4 with O2, was calculated first, the particles dynamics model written by C program was then integrated into flame by UDF to predict the particles＂ size. The effect of temperature and air flow rate on particles size dispersion was discussed based on the analytic results. It can be concluded that spherical particles form easily at high temperature;the longer particles stay in the flame, the bigger the average diameter will be; the dilution has certain effect on the growth.