In the last two decades, multidisciplinary research teams worked on developing a comprehensive understanding of the transmission mechanisms of airborne diseases. This article reviews the experimental studies on the characterization of the exhaled airflow and the droplets, comparing the measured parameters, the advantages, and the limitations of each technique. To characterize the airflow field, the global flow‐field techniques—high‐speed photography, schlieren photography, and PIV—are applied to visualize the shape and propagation of the exhaled airflow and its interaction with the ambient air, while the pointwise measurements provide quantitative measurements of the velocity, flow rate, humidity and temperature at a single point in the flow field. For the exhaled droplets, intrusive techniques are used to characterize the size distribution and concentration of the droplets' dry residues while non‐intrusive techniques can measure the droplet size and velocity at different locations in the flow field. The evolution of droplets' size and velocity away from the source has not yet been thoroughly experimentally investigated. Besides, there is a lack of information about the temperature and humidity fields composed by the interaction of the exhaled airflow and the ambient air.

中文翻译：

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呼出气流和液滴表征应用技术综述

在过去的二十年里，多学科研究团队致力于全面了解空气传播疾病的传播机制。本文回顾了关于呼出气流和液滴表征的实验研究，比较了每种技术的测量参数、优势和局限性。为了表征气流场，应用全局流场技术（高速摄影、纹影摄影和 PIV）来可视化呼出气流的形状和传播及其与环境空气的相互作用，而逐点测量提供定量测量流场中单个点的速度、流量、湿度和温度。对于呼出的飞沫，侵入式技术用于表征液滴干燥残留物的尺寸分布和浓度，而非侵入式技术可以测量流场中不同位置的液滴尺寸和速度。远离源头的液滴大小和速度的演变尚未经过彻底的实验研究。此外，还缺乏关于呼出气流与环境空气相互作用所组成的温湿度场的信息。