Thermodynamic analysis of the causes of micro-explosions of droplets in nanoparticle synthesis in spray flames

喷雾火焰合成纳米粒子的成功与否，关键取决于燃烧器内液滴微爆炸的发生。然而，这些微爆炸的原因还没有被很好地理解，并且提出了相互矛盾的解释。因此，我们项目的目的是澄清微爆炸的原因。工作假设是，微爆炸是由液滴内部的蒸发开始引起的。这是否会发生取决于刘易斯数，该数描述了液滴中的传热与传质的比率，从而取决于前体溶液的流体性质。为了实现项目目标，实验工作将与建模和仿真工作相结合。作为起点，将对文献中和SPP内部工作中关于微爆炸和由此产生的纳米颗粒的质量的实验结果进行全面调查。将编辑相应的流体性质数据，以便可以计算刘易斯数等。如有必要，将在本项目中使用本项目在第一个供资期间确定的方法来测量流体性质数据。此外，液滴内部开始沸腾的必要条件将由传热和传质模型确定，这一知识将应用于喷雾火焰合成系统。在与Mädler(不来梅)教授的合作中，对以前没有研究过的系统的预测将进行实验测试。对于选定的系统，本项目的液滴模拟将与Kronenburg(斯图加特)教授小组的详细气相模拟相结合，并与Mädler教授小组的实验结果进行比较。

The success of the spray flame synthesis of nanoparticles depends crucially on the occurrence of micro-explosions of the droplets in the burner. However, the cause of these micro-explosions is not yet well-understood and contradicting explanations have been proposed. The aim of our project is therefore to provide clarity on the causes of the micro-explosions. The working hypothesis is that the micro-explosions are caused by the onset of evaporation inside the droplet. Whether this can happen depends on the Lewis number, which describes the ratio of the heat transfer to the mass transfer in the droplet, and thus on the fluid properties of the precursor solution. To achieve the project goal, experimental work will be combined with work on modeling and simulation. As a starting point, a comprehensive survey of experimental results from the literature and from work within the SPP on micro-explosions and the quality of the resulting nanoparticles will be carried out. The corresponding fluid property data will be compiled, such that, among others, the Lewis numbers can be calculated. Where necessary, the fluid property data will be measured in the present project, using the methods that were established in the present project in the 1st funding period. Furthermore, the necessary conditions for the onset of boiling inside the droplet will be determined from a model of the heat and mass transfer, and that knowledge will be applied to the systems of the spray flame synthesis. In a co-operation with Prof. Mädler (Bremen), predictions for systems that have not been investigated before will be tested experimentally. For a selected system, droplet simulations from the present project will be combined with detailed gas phase simulations from the group of Prof. Kronenburg (Stuttgart) and compared to experimental results from the group of Prof. Mädler.