Biswas Riddhideep, Pal Anish, Pal Ritam, Sarkar Sourav, Mukhopadhyay Achintya
Department of Mechanical Engineering, Jadavpur University, Kolkata-700032, India.
Department of Mechanical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Phys Fluids (1994). 2022 Jan;34(1):013318. doi: 10.1063/5.0073694. Epub 2022 Jan 24.
Respiratory droplets-which may contain disease spreading virus-exhaled during speaking, coughing, or sneezing are one of the significant causes for the spread of the ongoing COVID-19 pandemic. The droplet dispersion depends on the surrounding air velocity, ambient temperature, and relative humidity. In a confined space like an elevator, the risk of transmission becomes higher when there is an infected person inside the elevator with other individuals. In this work, a numerical investigation is carried out in a three-dimensional domain resembling an elevator using OpenFoam. Three different modes of air ventilation, viz., quiescent, axial exhaust draft, and exhaust fan, have been considered to investigate the effect of ventilation on droplet transmission for two different climatic conditions (30 , 50% relative humidity and 10 , 90% relative humidity). The risk assessment is quantified using a risk factor based on the time-averaged droplet count present near the passenger's hand to head region (risky height zone). The risk factor drops from 40% in a quiescent scenario to 0% in an exhaust fan ventilation condition in a hot dry environment. In general, cold humid conditions are safer than hot dry conditions as the droplets settle down quickly below the risky height zone owing to their larger masses maintained by negligible evaporation. However, an exhaust fan renders the domain in a hot dry ambience completely safe (risk factor, 0%) in 5.5 s whereas it takes 7.48 s for a cold humid ambience.
在说话、咳嗽或打喷嚏时呼出的呼吸道飞沫（可能含有传播疾病的病毒）是当前新冠疫情传播的重要原因之一。飞沫扩散取决于周围空气流速、环境温度和相对湿度。在电梯这样的密闭空间中，当电梯内有感染者与其他人共处时，传播风险会更高。在这项工作中，使用OpenFoam在一个类似电梯的三维区域内进行了数值研究。考虑了三种不同的通风模式，即静止、轴向排风通风和排气扇通风，以研究在两种不同气候条件（30摄氏度、50%相对湿度和10摄氏度、90%相对湿度）下通风对飞沫传播的影响。使用基于乘客手部到头部区域（危险高度区域）附近的时间平均飞沫计数的风险因子对风险评估进行量化。在炎热干燥的环境中，风险因子从静止场景下的40%降至排气扇通风条件下的0%。一般来说，寒冷潮湿的条件比炎热干燥的条件更安全，因为由于蒸发可忽略不计而保持较大质量，飞沫会迅速沉降到危险高度区域以下。然而，排气扇能使炎热干燥环境中的区域在5.5秒内完全安全（风险因子为0%），而寒冷潮湿环境则需要7.48秒。
