The development of jet nebulizers for medical purposes is an important challenge of aerosol therapy. The performance of a nebulizer is characterized by its output rate of droplets with a diameter under 5 µm. However the optimization of this parameter through experiments has reached a plateau. The purpose of this study is to design a numerical model simulating the nebulization process and to compare it with experimental data. Such a model could provide a better understanding of the atomization process and the parameters influencing the nebulizer output. A model based on the Updraft nebulizer (Hudson) was designed with ANSYS Workbench. Boundary conditions were set with experimental data then transient 3D calculations were run on a 4 µm mesh with ANSYS Fluent. Two air flow rate (2 L/min and 8 L/min, limits of the operating range) were considered to account for different turbulence regimes. Numerical and experimental results were compared according to phenomenology and droplet size. The behavior of the liquid was compared to images acquired through shadowgraphy with a CCD Camera. Three experimental methods, laser diffractometry, phase Doppler anemometry (PDA) and shadowgraphy were used to characterize the droplet size distributions. Camera images showed similar patterns as numerical results. Droplet sizes obtained numerically are overestimated in relation to PDA and diffractometry, which only consider spherical droplets. However, at both flow rates, size distributions extracted from numerical image processing were similar to distributions obtained from shadowgraphy image processing. The simulation then provides a good understanding and prediction of the phenomena involved in the fragmentation of droplets over 10 µm. The laws of dynamics apply to droplets down to 1 µm, so we can assume the continuity of the distribution and extrapolate the results for droplets between 1 and 10 µm. So, this model could help predicting nebulizer output with defined geometrical and physical parameters.
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机译：用于医学目的的喷射喷雾器的开发是气雾疗法的重要挑战。雾化器的性能以直径小于5 µm的液滴的输出速率为特征。然而，通过实验对该参数的优化已达到平稳状态。这项研究的目的是设计一个模拟雾化过程的数值模型，并将其与实验数据进行比较。这样的模型可以更好地了解雾化过程和影响雾化器输出的参数。 ANSYS Workbench设计了基于Updraft雾化器（Hudson）的模型。使用实验数据设置边界条件，然后使用ANSYS Fluent在4 µm网格上进行瞬态3D计算。考虑了两种空气流速（2 L / min和8 L / min，工作范围的极限）来说明不同的湍流状态。根据现象学和液滴大小比较了数值和实验结果。将液体的行为与通过CCD相机通过阴影摄影获得的图像进行比较。三种实验方法，激光衍射法，相位多普勒风速仪（PDA）和影印术被用来表征液滴的大小分布。相机图像显示出与数字结果相似的图案。与仅考虑球形液滴的PDA和衍射法相比，通过数值获得的液滴尺寸被高估了。但是，在两种流速下，从数值图像处理中提取的尺寸分布与从皮影图像处理中获得的分布相似。然后，模拟可以很好地理解和预测10 µm以上的液滴破碎所涉及的现象。动力学定律适用于1 µm以下的液滴，因此我们可以假设分布的连续性，并推断1至10 µm之间的液滴的结果。因此，该模型可以帮助预测具有定义的几何和物理参数的雾化器输出。
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