Abstract
Breathing air that contains virus-infected droplets is the leading cause of Covid-19 transmission. Sneezing, coughing, breathing, and talking of an infected person would generate aerosolized droplets that carry the coronavirus. Earlier research efforts have focused on sneezing and coughing as the primary transmission sources. New experiments and field studies have shown that breathing and talking are also effective mechanisms in spreading viruses. In this article, the dispersion of particles/droplets during speaking is studied. COVID-19 virus is about 120 nanometers and is suspended in saliva or mucus droplets emitted by an injected person. These droplets evaporate in a fraction of a second as they enter the environment and reduce in size. However, the droplets’ viral content remains the same as they move by the room’s airflow. The particles from sneezing and coughing are larger than those released by speaking. As the particles/droplets are small, the effect of gravity is small, and they remain suspended in the air for a long time. Also, being small makes them more easily penetrate the respiratory passages.
Using the computational fluid dynamics method in conjunction with the ANSYS-Fluent software, the particle transport and dispersion were simulated. The Eulerian approach modeled the airflow (continuous phase), and the Lagrangian approach modeled the particle (discrete phase) movements. This study also investigated the ventilation system’s effects on the distribution of particles in the indoor environment. The displacement and mixing air distribution systems were considered. Simulation results showed that droplets remain suspended in the room for a relatively long time after evaporation. Large particles were deposited quickly, and a significant percentage of smaller particles were removed by the ventilation system. The concentration of particles in the upper half of the room was also quite low for the mixing ventilation system. This was due to the fact that the room air mixing system is relatively uniform; this uniformity of airflow caused the particles to get trapped quickly. Also, for the displacement system, the room airflow was not uniform; these particles were then dispersed in the room and spent more time in the indoor environment.
