Twin fluid atomizers allow for two different spray forming modes, flow focusing and flow blurring, depending on the operating, geometric, and thermophysical properties of the working liquids. In flow focusing mode, the liquid jet breaks outside the injector, whereas in flow blurring mode, the liquid jet breaks inside the atomizer. Operating conditions are believed to play an essential role in determining the size and velocity of droplets with specific geometric and fluid properties. This work investigates the effect of air flow rate and liquid flow rate on spray characteristics by varying them independently. The geometric parameters, height (H = 0.3 mm) and orifice diameter (D = 1.5 mm) of the atomizer are kept constant (with H/D = 0.2). Spray mode is identified using high-speed images. Phase Doppler particle analyzer is used to measure droplet size and velocity simultaneously. Regardless of liquid flow rate, flow focusing mode is observed at low air flow rate and flow blurring mode is observed at high air flow rate. In general, flow blurring mode produced smaller droplets at higher velocities than flow focusing mode. The Joint probability distribution function of droplet size and velocity shows unimodal near the exit of the atomizer and bimodal distribution around 50 mm downstream due to the completion of the secondary breakup around that position and the subsequent loss of momentum due to the resistance of the surrounding air from the injector outlet. Flow focusing mode showed that sauter mean diameter and mass median diameter tend to increase initially due to coalescence of the spray and begin to decrease due to secondary breakup. The joint probability distribution of droplet Weber number and the droplet Reynolds number indicate that the flow blurring spray produced finer and faster droplets than the flow focusing spray. Overlapping of two Gaussians representing smaller and larger droplets best fits the droplet probability distribution as compared to lognormal or gamma or beta distribution.

中文翻译：

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基于光学诊断工具的双流体雾化器液体喷射方式的实验研究

双流体雾化器允许两种不同的喷雾形成模式，流动聚焦和流动模糊，这取决于工作液体的操作、几何和热物理特性。在流动聚焦模式下，液体射流在喷射器外破裂，而在流动模糊模式下，液体射流在雾化器内部破裂。操作条件被认为在确定具有特定几何和流体特性的液滴的大小和速度方面起着至关重要的作用。这项工作通过独立地改变空气流速和液体流速对喷雾特性的影响进行研究。雾化器的几何参数、高度 (H = 0.3 mm) 和孔口直径 (D = 1.5 mm) 保持恒定 (H/D = 0.2)。喷雾模式使用高速图像识别。相位多普勒粒子分析仪用于同时测量液滴尺寸和速度。不管液体流速如何，在低空气流速下观察到流动聚焦模式，在高空气流速下观察到流动模糊模式。一般来说，流动模糊模式比流动聚焦模式以更高的速度产生更小的液滴。液滴尺寸和速度的联合概率分布函数在雾化器出口附近显示单峰分布，下游约 50 mm 处双峰分布，这是由于该位置周围的二次分裂完成以及随后由于周围空气阻力导致的动量损失从喷油器出口。流动聚焦模式表明，sauter 平均直径和质量中值直径最初由于喷雾的聚结而趋于增加，并由于二次破碎而开始减少。液滴韦伯数和液滴雷诺数的联合概率分布表明，流动模糊喷雾比流动聚焦喷雾产生更细、更快的液滴。与对数正态分布或 gamma 或 beta 分布相比，代表更小和更大液滴的两个高斯重叠最适合液滴概率分布。