火焰喷雾热解颗粒形成的理论单液滴模型
Theoretical single droplet model for particle formation in flame spray pyrolysis
摘要：
在目前的工作中，我们开发了一个单液滴模型来描述多组分液滴燃烧中的颗粒形成。研究了不同溶液性质的气-粒转化和液滴-粒转化途径，以及粒子数平衡模型和液滴干燥模型。对于不含前体的多组分液滴，液滴燃烧受到液相中物质扩散的限制。该模型可以很好地预测由以前的PDA测量观察到的液滴收缩的历史。对于具有比其热分解温度低的沸点的前体，液滴中的前体然后可以通过气-粒转化途径转化为纳米颗粒。粒子数平衡模型表明，生成的纳米粒子的大小依赖于前体的质量分数和停留时间，这是一致的蒸汽进料气溶胶火焰合成。对于倾向于在液体中分解或沉淀的前体，其然后经历液滴到颗粒的转化路线。液滴行为可以通过液滴蒸发时间与前驱体反应或沉淀时间的比率来分类。对于蒸发时间短的小液滴，纳米颗粒的形成遵循一滴一颗粒规则。对于蒸发时间长的大液滴，沉淀、热分解和蒸发之间的竞争决定了最终的纳米颗粒形态。本研究建立的单液滴模型可用于指导前驱体的设计，并可与整个火焰喷雾热解燃烧器的湍流火焰模拟相耦合。
英文摘要：
In the current work, we develop a single droplet model to describe particle formation in multicomponent-liquid droplet combustion. Both the gas-to-particle conversion and droplet-to-particle conversion routes of different solution properties are investigated, together with the population balance model and the droplet drying model. For multi-component droplets without precursors, the droplet combustion is limited by the species diffusion in the liquid phase. The model can well predict the droplet shrinkage history observed by previous PDA measurements. For the precursor with a low boiling point than its thermal decomposition temperature, the precursor in the droplet can then transform into nanoparticles through the gas-to-particle conversion route. The population balance model reveals that the generated nanoparticle size relies on both the precursor mass fraction and the residence time, which is consistent with the vapor-fed aerosol flame synthesis. For the precursor that tends to decompose or precipitate in the liquid, it then undergoes the droplet-to-particle conversion route. The droplet behavior can be classified by the ratio of droplet evaporation time and precursor reaction or precipitation time. For small droplets with short evaporation time, the nanoparticle formation obeys the one-droplet-one-particle rule. For large droplets with long evaporation time, the competition among precipitation, thermal decomposition, and evaporation determines the final nanoparticle morphology. The single droplet model established in this study can potentially guide the precursor design and be coupled with the turbulent flame simulation of the whole flame spray pyrolysis burner.
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