Modeling Evaporation of Water Droplets as Applied to Survival of Airborne Viruses

Abstract

Many viruses, such as coronaviruses, tend to spread airborne inside water microdroplets. Evaporation of the microdroplets may result in a reduction of their contagiousness. However, the evaporation of small droplets is a complex process involving mass and heat transfer, diffusion, convection and solar radiation absorption. Virological studies indicate that airborne virus survival is very sensitive to air humidity and temperature. We employ a model of droplet evaporation with the account for the Knudsen layer. This model suggests that evaporation is sensitive to both temperature and the relative humidity (RH) of the ambient air. We also discuss various mechanisms such as the effect of solar irradiation, the dynamic relaxation of moving droplets in ambient air and the gravitational sedimentation of the droplets. The maximum estimate for the spectral radiative flux in the case of cloudless sky showed that the radiation contribution to evaporation of single water droplets is insignificant. We conclude that at small and even at moderately high levels of RH, microdroplets evaporate within dozens of seconds with the convective heat flux from the air being the dominant mechanism in every case. The numerical results obtained in the paper are in good qualitative agreement with both the published laboratory experiments and seasonal nature of many viral infections. Sophisticated experimental techniques may be needed for in situ observation of interaction of viruses with organic particles and living cells within microdroplets. The novel controlled droplet cluster technology is suggested as a promising candidate for such experimental methodology.

Indoor transmission dynamics of expired SARS-CoV-2 virus in a model African hospital ward

“…the more particles are able to travel along their path, the longer their residence time in the air. The smaller droplets would understandably have longer residence time than the larger droplets [29,30]. How far could sneezes or cough droplets travel in the air?…”

Survival of Virus Particles in Water Droplets: Hydrophobic Forces and Landauer’s Principle

“…Since viruses do not maintain homeostasis, they rely on an external stabilizing by the thermal reservoir formed by an aquatic environment. Drying of microdroplets containg viruses is viewed as an important mechanism to limit the spreading of viral respiratory diseases [49,50].…”

“…Interactions that control the self-assembly of the droplet cluster are water phase transitions (condensation and evaporation) and aerodynamic forces from the flow of a mixture of water vapor and ambient air [ 47 ]. The water cluster can be used for in situ monitoring of airborn microdroplets containing small biological objects [ 48 , 49 ]. Thus, living cells are adsorbed at the liquid–gas phase interface due to hydrophobic forces, which are also crucial for the cell membrane ( Figure 5 ).…”

The Concept of a Compound Autopsy Experimental Laboratory for SARS-CoV-2 Aerosolization Studies

“…However, it would be impossible to employ a nebulizer on the autopsy experimental platform because, apparently, SARS-CoV-2 studies would require more sensitive samplers. For example, employing an investigation model of droplet bioaerosols in stabilized droplet clusters with a Axio Zoom V16 fluorescence microscope [9] or laser light-scattering experiments [10]. Those are only examples of an experimental platforms without specification of the details of the methodology that would be superfluous in the presentation of the concept.…”