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

在火焰喷雾合成中，液体到气体的转移和随后的颗粒生长在很大程度上仍然是一个未被探索的研究领域。在这里，缺乏合适的实验和数值方法来描述这种相变的所有细节。因此，从喷雾到颗粒的链中的关键工艺步骤仍然是推测的。该项目的目标是对火焰喷雾反应器中液体(液滴)相到固体(颗粒)相的转变进行详细的研究。因此，将使用实验工具和数值工具相结合，两者相辅相成。这些研究的目的是为了研究颗粒相中液体/液滴相的转变，从而更好地了解颗粒形成的机理。这使得能够确定有效的火焰喷雾合成的关键参数，然后可以用于工艺的优化和放大。第一个项目阶段专注于低火焰区域颗粒形成机制的建模。流体动力学模拟得到了颗粒形成区温度和浓度梯度的数据。这些数据的应用导致了对粒子形成模型的重新解释。事实证明，颗粒大小测定方法适用于从形成初级颗粒的低火焰区域取样。申请者之间的密切合作使喷雾火焰中粒子形成的基本过程得以专题覆盖：Kruis小组专注于与粒子动力学相关的复杂的特定过程，而Thévenin小组详细研究喷雾、蒸发和反应气相；这两个数值项目都受益于Wigger小组在比较和验证意义上的系统实验，也给建模方法带来了新的问题。在第二阶段，将调查先导火焰和弥散气体的组成的影响；此外，还将调查替代溶剂。数值模型将扩展到多组分蒸发、液相反应和详细考虑靠近液滴的气相。为了支持我们对疑似微爆炸原因的理解，喷雾燃烧的稳定性将用DNS和双种群蒙特卡罗方法进行研究。

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.