Abstract Understanding the role of human expiratory flows on respiratory infection in ventilated environments is useful for taking appropriate interventions to minimize the infection risk. Some studies have predicted the lock-up phenomenon of exhaled flows in stratified environments; however, there is a lack of high-quality experimental data to validate the theoretical models. In addition, how thermal stratification affects the transport of exhaled particles has not been explored so far. In this study, a water tank experiment was conducted according to the similarity protocols to mimic how the expiratory airflow and particles behaved in both uniform and stratified environments. The lock-up phenomenon was visualized and compared with the predicted results by an integral model. Results showed that our previously developed theoretical model of a respiratory airflow was effective to predict the airflow dispersion in stratified environments. Stratification frequency (N) of the background fluid and the Froude Number F r 0 of the thermal flow jointly determined the lock-up layer in a power law. For the particle dispersion, it indicated that small particles such as fine droplets and droplet nuclei would be ‘locked’ by indoor thermal stratification, and disperse with the thermal flow over a long distance, potentially increasing the long-range airborne infection risk. Large particles such as large droplets can deposit within a short distance, hardly affected by thermal stratification, however, droplet infection could happen to the susceptible people at a close contact with the infector. This study could give some guidance in view of cross-infection control indoors for stratified environment.

中文翻译：

---

室内分层环境中呼气气流和颗粒扩散的实验室研究

摘要 了解人呼气流量在通风环境中对呼吸道感染的作用有助于采取适当的干预措施将感染风险降至最低。一些研究预测了分层环境中呼出气流的锁定现象；然而，缺乏高质量的实验数据来验证理论模型。此外，到目前为止还没有探索热分层如何影响呼出颗粒的传输。在这项研究中，根据相似性协议进行了水箱实验，以模拟呼气气流和颗粒在均匀和分层环境中的行为。通过积分模型将锁定现象可视化并与预测结果进行比较。结果表明，我们之前开发的呼吸气流理论模型可有效预测分层环境中的气流分散。背景流体的分层频率 (N) 和热流的弗劳德数 F r 0 共同决定了幂律中的锁定层。对于颗粒分散，表明细小液滴和液滴核等小颗粒会被室内热分层“锁定”，并随热流远距离分散，可能增加远距离空气传播的感染风险。大飞沫等大颗粒可以在短距离内沉积，几乎不受热分层影响，但与感染者密切接触的易感人群可能发生飞沫感染。