In flame spray pyrolysis (FSP), the understanding of the atomization and spray formation of the coaxial atomizer is a key step to control the mixing of reactants, and precursor release, as well as nanoparticle formation and growth mechanisms. The drop size and drop dynamics of fuel/precursor mixtures are relevant parameters to control the particle synthesis via gas-to-particle conversion for tailoring the nanoparticle. The investigation of the multiphase flow structures, especially in the dense spray region using sophisticated nonintrusive laser diagnostics, such as phase Doppler anemometry (PDA), enables a characterization of the burner with multiscale spatial and temporal resolution. In the present work, the evolution of drop size and velocity under varying iron nitrate (FNT) concentration of the precursor is investigated allowing for an estimation of precursor release and evaporation via detailed PDA measurements. The drop size distributions of pure ethanol, and ethanol + 2-ethylhexanoic acid, as well as for FNT-based spray flames, were studied in order to reveal the influence of metal precursors on the combustion. Drop size/velocity correlations were determined in order to resolve the size class averaged evolution of drop velocities. The evolution of the drop size distribution along the axial centerline revealed a variation of the evaporation rate in space and increased evaporation rates for FNT containing spray flames. Furthermore, bimodal drop size distributions were observed for heights above the burner larger than 40 mm in FNT precursor spray flames, indicating the occurrence of possible μ-explosions of drops, that have been reported in the literature for similar systems but only in single-droplet experiments so far.

中文翻译：

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异质喷雾合成纳米颗粒的液滴动力学

在火焰喷雾热解（FSP）中，了解同轴雾化器的雾化和喷雾形成是控制反应物混合，前体释放以及纳米颗粒形成和生长机制的关键步骤。燃料/前体混合物的液滴尺寸和液滴动力学是相关参数，以通过用于定制纳米颗粒的气体-颗粒转化来控制颗粒合成。使用复杂的非侵入式激光诊断技术（例如相位多普勒风速计（PDA））对多相流结构进行研究，尤其是在浓雾区域，能够以多尺度的时空分辨率表征燃烧器。在目前的工作中，研究了在不同浓度的前驱硝酸铁（FNT）下液滴尺寸和速度的变化，从而可以通过详细的PDA测量估算前驱物的释放和蒸发。研究了纯乙醇和乙醇+ 2-乙基己酸以及基于FNT的喷雾火焰的液滴尺寸分布，以揭示金属前驱物对燃烧的影响。确定液滴大小/速度的相关性，以便解决液滴速度的大小类平均演变。沿轴向中心线的液滴尺寸分布的演变揭示了空间蒸发速率的变化以及含FNT喷雾火焰的蒸发速率增加。此外，液滴的μ爆炸，在文献中已经报道过类似系统，但到目前为止仅在单液滴实验中。