Evaporation flow characteristics of respiratory droplets: Dynamic property under multifarious ambient conditions

Abstract

This study numerically investigated the impact of ambient conditions on the evaporation process of full-range cough expelled droplets. The multi-component Eulerian-Lagrangian framework was adopted to simulate droplet evaporation within the inhomogeneous humidity fields. The results found that effect of ambient relative humidity (RH) on droplet evaporation was more pronounced than that of temperature. When the ambient relative humidity was higher than 40%RH, the evaporation of droplets with a diameter smaller than 100 μm would be significantly decelerated. Meanwhile, in normal indoor environments, 175μm could be a marginal diameter, in which droplets with larger initial diameters would probably not be fully evaporated before settling to the ground. Moreover, a novel cost-efficient approach, representing the instantaneous droplet diameter by functions of dt=φ(RH,t,T), was developed to fulfil the time-dependent dynamic size distributions of evaporated droplets under various ambient conditions directly from the data by this study. The implementation of this approach into User Defined Function (UDF) was demonstrated and it would significantly reduce the computational resource on simulating droplet-related scenarios as it does not require costly calculations on the evaporation processes of each droplet repeatedly in every simulation. This development is limited to cough droplets so far and further fulfilment on droplets database regarding other respiratory behaviours would be highly suggested.