Nanoparticle formation from precursor-loaded droplets: flow dynamics, population dynamics of particles and droplets, experimental validation.

在火焰喷射合成中，液体到气体的转移和随后的颗粒生长仍然是一个很大程度上未开发的研究领域。在这里，合适的实验以及描述这种相变的所有细节的数值方法是缺乏的。因此，从喷雾到颗粒链中的关键工艺步骤仍然是推测性的。该项目的目标是对火焰喷雾反应器中从液体（液滴）相到固体（颗粒）相的转变进行详细的研究。因此，将使用实验和数值工具的组合，这两者完美地相互补充。这些旨在研究从液体/液滴相到颗粒相的转变，从而更好地理解颗粒形成机制。这使得能够识别有效的火焰喷涂合成的关键参数，然后可以用于优化和放大工艺。第一个项目周期的重点是在较低的火焰区域的颗粒形成机制的建模。流体动力学模拟产生了颗粒形成区的温度和浓度梯度数据。这些数据的应用导致了对颗粒形成模型的重新解释。粒度测定方法证明适用于从初级颗粒形成的较低火焰区域取样。申请人之间的密切合作允许喷雾火焰中颗粒形成的基本过程的主题覆盖：Kruis小组专注于与颗粒动力学相关的复杂特定过程，而Thévenin小组详细研究喷雾，蒸发和反应气相;这两个数值项目在比较和验证的意义上都受益于Wiggers组的系统实验，在第二阶段，将研究引燃火焰和弥散气体的组成的影响;此外，还将研究替代溶剂。数值模型将扩展多组分蒸发，反应在液相中，并详细考虑气相接近液滴。喷雾燃烧的稳定性将与DNS以及与双人口蒙特-卡罗方法进行研究，以支持我们的理解可疑的微爆炸的原因。

In flame spray synthesis, the liquid-to-gas transfer and subsequent particle growth is a still largely unexplored research area. Here, both suitable experimental as well as numerical methods which describe this phase transformation in all details are lacking. As a result, key process steps in the chain from spray to particle remain speculative. This project has formulated the goal to perform a detailed investigation of the transition from the liquid (droplet) phase to the solid (particle) phase in a flame spray reactor. Therefore, a combination of experimental and numerical tools will be used, which perfectly complement each other. These aim at investigating the transition from the liquid/droplet phase in the particle phase and thereby gaining a better understanding of the particle formation mechanisms. This allows to identify the key parameters for an efficient flame spray synthesis, which can then be used for optimization and scaling-up of the process.The first project period focused on the modeling of the particle formation mechanisms in the lower flame region. The fluid dynamics simulations yielded data on the temperature and concentration gradients in the particle formation zone. The application of these data led to a re-interpretation of the particle formation models. The particle sizing methods proved suitable for sampling from the lower flame region, where primary particles form. The close collaboration between the applicants allows a thematic coverage of the essential processes in particle formation in spray flames: the Kruis group focuses on the complex particular processes relevant for the particle dynamics, whereas the Thévenin group investigates the spray, the evaporation and the reactive gas phase in detail; both numerical projects benefit from the systematic experiments of the Wiggers group in the sense of comparison and validation, also leading to new questions for the modeling approach.In the second period the influence of the composition of the pilot flame and the dispersion gas will be investigated; furthermore, alternative solvents will be investigated. The numerical models will be extended with multicomponent evaporation, reactions in the liquid phase and detailed consideration of the gas-phase close to the droplets. The stability of the spray combustion will be investigated with DNS as well as with the dual-population Monte-Carlo method, in order to support our understanding of the cause of the suspected micro explosions.