Numerical calculation of necessary distancing regarding SARS-CoV-2 (COVID-19) vs. spherical viruses, based on environmental features

Corona viruses are spherical nanoparticles with peripheral spike protein and diameters around 60 to 140 nm. In contrast to the elder versions, COVID-19 spread vastly and quickly all over the world. World Health Organization (WHO) insists on adequate social distancing in order to decrease the risk of contagion by air. In the present work, different parameters which affect the necessary social distance were investigated. Drag coefficient around a Corona-shaped nanoparticle with the geometry of COVID-19 was determined by modeling laminar flow in different Reynolds numbers. Accordingly, modified correlations for drag coefficient were derived which implied to be much higher in Corona-shaped particles in compare to spherical ones. Applying the new modified correlation, the behavior of 120 nm to 120 m droplets generated by sneezing or coughing were investigated considering the evaporation of the volatile portion of the virus (around 94%), in different ambient conditions, namely temperature, pressure and relative humidity. Studying COVID-19 falling behavior showed that terminal velocity in Corona-shaped particles was much lower than spherical particles of the same size. It was also proved that falling time in Corona-shaped particles was longer, i.e. lasted longer in air. Ambient temperature increase and decrease in ambient relative humidity resulted into decrease in falling speed of the Corona particles. Decrease in ambient pressure, i.e. increase in elevation from sea level, yielded an increase in molecular free mean path which consequently resulted into reduction in falling speed. Hot dry areas were recognized to be critical from the viewpoint of COVID-19 spread through air.