Abstract

The SARS-CoV-2 pandemic has heightened the interest in particle-laden turbulent jets generated by breathing, talking, coughing and sneezing, and how these can contribute to disease transmission. We present quantitative measurement methods for such flows, while exploring and offering improvements for common shortcomings. We generate jets consisting of either liquid droplets or solid particles in an isothermal, quiescent and electrically isopotential experimental chamber that was constructed to control the effects of ambient forcing on jet behavior. For liquid droplets, we find promise in surface deposition analysis based on fluorescent tracer use. For particles, we explore the performance of commercially available adhesive sampling strips and develop conductive grounded carbon tape based sampling strips. We explore ways in which the smallest of thermal gradients or electrostatic charge issues can affect particle dispersion, and suggest practical methods to address these issues. The developed methods are applied to study the simultaneous deposition of $\approx$ 25, 50 and 200 μm solid particles from a particle laden turbulent jet with a mean velocity of 33.2 m/s. The deposition location as a function of particle size was compared to results from a simple numerical RANS model, and illustrates ways in which imprecise initial or boundary conditions can lead to a notable deviation from experimental results. The differences in deposition pattern seen in experimental and numerical results despite a carefully controlled environment and characterized particle ejection indicate the need for a more stringent numerical model validation, especially when studying fate and transport of mid-range (neither purely aerosol or ballistic) sized particles.

摘要

SARS-CoV-2 大流行提高了人们对呼吸、说话、咳嗽和打喷嚏产生的载有颗粒的湍流喷射以及这些如何促进疾病传播的兴趣。我们提出了此类流量的定量测量方法，同时探索并提供了常见缺点的改进。我们在等温、静态和电等电位实验室中产生由液滴或固体颗粒组成的射流，该实验室旨在控制环境力对射流行为的影响。对于液滴，我们在基于荧光示踪剂的表面沉积分析中找到了希望。对于颗粒，我们探索了市售粘性采样条的性能，并开发了基于导电接地碳带的采样条。我们探索了最小的热梯度或静电荷问题会影响颗粒分散的方式，并提出解决这些问题的实用方法。所开发的方法用于研究同时沉积$\approx$来自平均速度为 33.2 m/s 的载有颗粒的湍流射流的 25、50和 200  μm固体颗粒。将作为粒径函数的沉积位置与来自简单数值 RANS 模型的结果进行比较，并说明不精确的初始或边界条件可能导致与实验结果显着偏差的方式。尽管仔细控制环境和表征粒子喷射，但在实验和数值结果中看到的沉积模式差异表明需要更严格的数值模型验证，尤其是在研究中程（非纯气溶胶或弹道）大小粒子的命运和传输时.