Paik Samuel Y, Vincent James H
Department of Environmental Health Sciences, School of Public Health, University of Michigan, Ann Arbor, MI 48109-2029, USA.
Ann Occup Hyg. 2004 Jan;48(1):3-11. doi: 10.1093/annhyg/meg088.
This paper describes two sets of experiments that were intended to characterize the orientation-averaged aspiration efficiencies of IOM samplers mounted on rotating bluff bodies. IOM samplers were mounted on simplified, three-dimensional rectangular bluff bodies that were rotated horizontally at a constant rate. Orientation-averaged aspiration efficiencies (A360) were measured as a function of Stokes' number (St), velocity ratio (R) and dimension ratio (r). Aspiration efficiency (A) is the efficiency with which particles are transported from the ambient air into the body of a sampler, and A360 is A averaged over all orientations to the wind. St is a dimensionless variable that represents particle inertia, R is the ratio of the air velocity in the freestream and that at the plane of the sampler's entry orifice, and r is the ratio of the sampler's orifice diameter and the bluff body's width. The first set of experiments were instrumental in establishing a hierarchy of effects on orientation-averaged A. It was clear that compared to r, St had a much larger influence on A. It was also clear, however, that the effects of St were overpowered by the effects of R in many cases. As concluded in previous studies, R and St were considered the most important factors in determining A, even for A360. The second set of experiments investigated A360 of IOM samplers for a much wider range of r than examined in previous research. Two important observations were made from the experimental results. One was that the A360 of IOM samplers, as a function of St, did not change for an r-range of 0.066-0.4. This meant that an IOM sampler mounted on a near life-size mannequin would measure the same aerosol concentration as one not mounted on anything. The second observation was that the aspiration efficiency curve of the IOM sampler was close to the inhalability curve. This gave further evidence that the bluff body did not play a major role in influencing A360, as the IOM samplers, in these experiments, were either mounted on miniature bluff bodies or on nothing at all. These observations all suggest that it is quite possible to design and test personal samplers with desired sampling characteristics using protocols that do not require full-size mannequins, which greatly simplifies the development of new samplers.
本文描述了两组实验，旨在表征安装在旋转钝体上的撞击式分级空气采样器（IOM）的取向平均抽吸效率。IOM采样器安装在简化的三维矩形钝体上，该钝体以恒定速率水平旋转。测量了取向平均抽吸效率（A360）作为斯托克斯数（St）、速度比（R）和尺寸比（r）的函数。抽吸效率（A）是颗粒从周围空气传输到采样器主体的效率，A360是在所有风向取向上的A平均值。St是一个无量纲变量，表示颗粒惯性，R是自由流中的空气速度与采样器入口孔平面处的空气速度之比，r是采样器孔直径与钝体宽度之比。第一组实验有助于建立对取向平均A的影响层次结构。很明显，与r相比，St对A的影响要大得多。然而，同样明显的是，在许多情况下，St的影响被R的影响所压倒。正如先前研究得出的结论，即使对于A360，R和St也被认为是决定A的最重要因素。第二组实验研究了IOM采样器在比先前研究中更广泛的r范围内的A360。从实验结果中得出了两个重要观察结果。一个是，IOM采样器的A360作为St的函数，在0.066 - 0.4的r范围内没有变化。这意味着安装在接近真人大小人体模型上的IOM采样器测量的气溶胶浓度与未安装在任何物体上的采样器相同。第二个观察结果是，IOM采样器的抽吸效率曲线接近可吸入性曲线。这进一步证明钝体在影响A方面没有起到主要作用，因为在这些实验中，IOM采样器要么安装在微型钝体上，要么根本没有安装任何东西。这些观察结果都表明，使用不需要全尺寸人体模型的方案来设计和测试具有所需采样特性的个人采样器是完全可能的，这大大简化了新采样器的开发。
