High-fidelity modeling of the drying kinetics, lifetimes, and trajectories of saliva droplets

• Applicant: Dr.-Ing. Holger Grosshans
• Subject Area: Fluid Mechanics
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468822780

So far, simple physical models are used to evaluate the drying and spreading of saliva droplets. These models support the critical conclusion that large droplets, which carry most viral copies, cause most Covid infections. These large droplets settle fast, so there is no danger as long as we keep a distance of two meters to other persons. However, the high number of infections in Germany during the lockdown since November 2020 implies that these assumptions are not justified. Instead, large droplets might dry into small particles which are light enough to be transported airborne over large distances and cause indirect virus transmission. Since the viral copies do not evaporate, these small particles might be the most dangerous ones. In previous projects, we have developed advanced numerical models for droplet evaporation and particle formation. Also, we developed a CFD tool for the transport of droplets and particles by turbulent airflow. In the proposed project, we will adapt the existing models to drying saliva and assemble them into one tool. This tool reflects the detailed droplet drying kinetics, including modifying the evaporation rate due to the solutes and forming a solid layer on the droplet surface. Such an approach is superior to the classical D-square model and will predict possible hollow particles. We collaborate with Prof. Berrocal (Lund University), who has unique expertise and one of the world-leading spray imaging laboratories. Prof. Berrocal provides simultaneous measurements of the droplet number, size, and velocity when a person is speaking, coughing, or sneezing, using imaging techniques of high detection sensitivity and spatial resolution. From this experimental data, we will generate accurate input conditions for our simulations of the virus transmission in a room. Such detailed simulations will lead to a better understanding of the saliva droplet drying kinetics and the virus transmission in specific situations. This project's results can lead to the re-evaluation of Covid protection guidelines, especially the two meters distancing rule. Hence, we contribute to managing the current and future pandemics.

• DFG Programme: Research Grants
• International Connection: Sweden
• Cooperation Partner: Dr. Edouard Berrocal