The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10−2 ⩽ Re ⩽ 103). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio (L¯), with the effect of the Reynolds number (Re) being significant only at low L¯. δ also increased with increasing dimensionless bronchiole diameter (D¯), but it is invariant with the particle size based Reynolds number. We show that δL¯∼Re−2 for 10−2 ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δL¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.

中文翻译：

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幻肺细支气管呼吸气溶胶输送的实验研究


微米级颗粒在肺部的运输和沉积是冠状病毒病 19 (COVID-19) 等气溶胶传播疾病传播的主要机制。考虑到目前的情况，对人肺细支气管中液滴的运输和沉积进行建模对于确定其对人类健康的影响至关重要。目前的研究报告了对模拟整个肺中粒子动力学的大范围 Re 的微毛细血管（代表远端肺细支气管）沉积的实验观察。该实验研究了直径范围为 0.3 mm 至 2 mm 且雷诺数范围较广 (10−2 ⩽ Re ⩽ 103) 的管中的沉积情况。本研究中使用的管直径和 Re 的范围是由肺气道的尺寸和典型的呼吸流速决定的。气溶胶流体负载有作为荧光团的硼掺杂碳量子点。使用超声波雾化器从这种混合流体中产生气溶胶羽流，产生平均直径为 6.5 µm 且尺寸分布较窄的液滴。使用分光荧光计测量沉积在管壁上的气溶胶的量。实验结果表明，无量纲沉积（δ）与细支气管纵横比（L´）成反比，雷诺数（Re）的影响仅在低L´时才显着。 δ 也随着无量纲细支气管直径 (D´) 的增加而增加，但它与基于雷诺数的颗粒尺寸保持不变。我们证明 δL∼Re−2 对于 10−2 ⩽ Re ⩽ 1，这是典型的扩散主导状态。对于 Re ⩾ 1，在撞击主导的情况下，δL¯ 与 Re 无关。我们还展示了一种交叉机制，其中沉积变得很重要。 实验结果得出结论，较低的呼吸频率和较长的屏气时间会显着增加在拥挤的地方感染 COVID-19 的机会。