Numerical simulation and experimental characterization of nanoparticle synthesis in flame spray processes

火焰喷射合成为定制纳米颗粒的生产提供了许多可能性。然而，喷雾、湍流、相变、前驱体分解、化学和颗粒形成的相互作用是如此复杂，我们对这一过程的理解相当不完整。在第一个供资期间，商定了一个参考燃烧器、参考条件和材料系统。开发了用于描述复杂过程的实验和模型。在第二个资助期，实验和模型将被扩展，并适应优化的参考燃烧器和新材料系统。参考燃烧器的新设计现在需要使用各种实验技术（粒子图像测速、相位多普勒测速、激光诱导荧光、弹性光散射和多角度光散射）进行表征。这些方法单独在多相系统中仅部分有用。因此，将影像诊断和数值模拟相结合的优势在资助期1中发展起来，将应用于粒子诊断。为了对模型进行有意义的验证，尽管存在固有的模糊性，我们将直接将数值模拟产生的合成信号与实验信号进行比较。该模型基于一种称为多重映射条件（MMC）的随机方法。这种方法允许对所涉及的所有过程（包括它们之间的相互作用）进行详细而有效的描述。随着FP1的结果和参考系统的预期变化，新的挑战出现了。需要定义新的边界条件，新的喷嘴设计包括分散气体的部分预混，可能需要扩展模型，以允许分层火焰的描述。此外，对纳米颗粒输运的描述应与气相的输运分离，以解释两相的不同扩散通量。最后，对前驱体-溶剂混合物的微爆炸进行了研究。在单液滴实验中，对SPP的大多数标准材料体系进行了微爆炸的报道，可以认为，基于相平衡的传统蒸发模型不能足够准确地描述蒸发通量。因此，应首次在实验中验证SpraySyn配置中微爆炸的发生，并在模拟中开发和实现描述该过程的半经验模型。

Flame spray synthesis offers numerous possibilities for the production of custom-made nanoparticles. However, the interactions of spray, turbulence, phase transition, precursor decomposition, chemistry and particle formation are so complex that our understanding of the process is rather incomplete. During the first funding period, a reference burner and reference conditions and material systems were agreed upon. Experiments and models for the description of the complex processes were developed. In the second funding period, experiments and models shall be extended, and adapted for the optimised reference burner and new material systems. The new design of the reference burner now needs to be characterised using a variety of experimental techniques (Particle Image Velocimetry, Phase-Doppler Anemometry, Laser-induced Fluorescence, Elastic Light Scattering and Multiple-Angle-Light –Scattering). These methods alone are only partially useful in multi-phase systems. Hence, the advantages of combining imaging diagnostics and numerical simulations developed in funding period 1, will be applied for particle diagnostics. In order to achieve meaningful validation of models, despite the inherent ambiguities, we will compare synthetic signals, generated by the numerical simulations directly with experimental signals. The modelling is based on a stochastic method called Multiple Mapping Conditioning (MMC). This method allows for a detailed and efficient description of all processes involved including their interactions. Following the results of FP1 and the expected changes of the reference system, new challenges arise. New boundary conditions need to be defined and the new nozzle design including partial premixing of the dispersion gases may require an extension of the modelling that allows for the description of stratified flames. Furthermore, the description of the transport of nanoparticles shall be decoupled from transport for the gaseous phase to account for the different diffusive fluxes of the two phases.Finally, the – so far mostly ignored – microexplosions of the precursor-solvent mixtures will be investigated. Microexplosions were reported for the most standard material systems of the SPP in single droplet experiments and it can be assumed, that conventional evaporation models, based on phase equilibria – cannot describe the evaporative fluxes with sufficient accuracy. Hence, the occurrence of microexplosions in the SpraySyn configuration shall be verified experimentally for the first time and semi-empirical models for the description of this process shall be developed and implemented in the simulations.