The motion of respiratory droplets produced by coughing

Abstract

Coronavirus disease 2019 has become a global pandemic infectious respiratory disease with high mortality and infectiousness. This paper investigates respiratory droplet transmission, which is critical to understanding, modeling, and controlling epidemics. In the present work, we implemented flow visualization, particle image velocimetry, and particle shadow tracking velocimetry to measure the velocity of the airflow and droplets involved in coughing and then constructed a physical model considering the evaporation effect to predict the motion of droplets under different weather conditions. The experimental results indicate that the convection velocity of cough airflow presents the relationship t −0.7 with time; hence, the distance from the cougher increases by t 0.3 in the range of our measurement domain. Substituting these experimental results into the physical model reveals that small droplets (initial diameter D ≤ 100 μ m) evaporate to droplet nuclei and that large droplets with D ≥ 500 μ m and an initial velocity u 0 ≥ 5 m/s travel more than 2 m. Winter conditions of low temperature and high relative humidity can cause more droplets to settle to the ground, which may be a possible driver of a second pandemic wave in the autumn and winter seasons.

Effects of surgical masks on droplet and aerosol dispersion under various oxygen delivery modalities

“…In this study, we performed two experiments in different oxygen delivery modes and modalities. Based on the particle visualization study, we found that visible droplets reached 60–80 cm while speaking and 1 m while coughing in a sitting position; the findings are similar to those in a recent study (13). In addition, these findings support results in a systematic meta-analysis, which showed that a physical distance of 1 m or more is optimum to reduce person-to-person virus transmission and to keep healthcare workers from contracting the SARS-CoV-2 infection (14).…”

Effects of slope and speed of escalator on the dispersion of cough-generated droplets from a passenger

“…In addition, an evaporation model 39 is implemented to model the mass and the diameter ( D ) change of droplets as follows: where D is the droplet diameter, M L is the molecular weight of water (0.018 kg/mole), is the average diffusion coefficient for vapor molecules in the saturated film around the droplet, is the density of water, J/(mol K) is the gas constant, T f is the temperature in the saturated film around the droplet, Re is Reynolds' number, Sc is Schmidt's number, and is the difference between the vapor pressure near the droplet and that in the ambient atmosphere. According to a recent study, 40 this model can estimate well the evaporation of cough-generated droplets in motion. These parameters are dependent on the environment temperature T and relative humidity ( RH ), which are chosen as C and in this study, representing a winter indoor environment approximately.…”

Effects of space sizes on the dispersion of cough-generated droplets from a walking person

“…The oval shape deformation of the droplet cloud can be explained as a result of different advancing and settling velocities of droplets of different sizes. 21 At t = 2.0 s, the cloud drops approximately to the waist height and deforms into an elongated shape that expands horizontally for both cases. Significant differences between the two cases are observed starting from this instant.…”