Session V24: Fluid Physics of Diseases Transmission

Live

The main transmission mode of the COVID-19 disease is through virus-laden aerosols and droplets generated by expiratory events, such as talking or sneezing. While the aerodynamics of such droplets have been the main focus of human studies, very little is known about their final deposition. To address this, we investigate mucosalivary dispersal and deposition onto horizontal surfaces corresponding to human exhalations with physical experiments under still-air conditions. Synthetic fluorescence tagged sprays with size and speed distributions comparable to human sneezes are observed with high-speed imaging. We systematically vary the rheological properties of the mucosaliva corresponding to healthy and non-healthy adults. Upon generating droplets with a synthetic sneeze, we measure its volumetric spatial-temporal dynamics on a horizontal surface. The results from this study will provide insight on how infectious diseases spread and further inform new strategies for social distancing.   

Live

A clear understanding of aerosol transport in different environments is crucial to find physics-informed measures for COVID-19 spreading mitigation. In this study, we investigated aerosol transport and surface deposition in a realistic classroom environment using Computational Fluid Dynamics (CFD) simulations. An instructor and nine students were placed in a 9 m by 9 m classroom, 2.4 m apart, following the social distance recommendations. A real situation of the room ventilation was applied by considering the classroom air conditioning according to ASHRAE 62.1 ventilation standards. Four different parameters including the particle size, aerosol source location, presence of sneeze guards in front of students, and the window state open vs. closed were studied. It is found that a significant fraction (24 – 50%) of particles smaller than 15 μm exit the classroom through the return diffusers of the air conditioning system within 15 minutes. This highlights the importance of effective filtration and sterilization systems within air conditioners. Sneeze guards are found to reduce the aerosol transmission of the 1 μm particles from the source to others by ~92%. By opening windows, the particle exit fraction can be increased by ~38% and aerosol deposition on people in the room is reduced.   

On Demand

COVID-19 has reached a pandemic level worldwide, becoming the greatest concern of the scientific community to unveil the biological and physical phenomena of viral transmission. However, the exact contribution of respiratory droplets to the transmission of respiratory diseases is still unclear. Here we aim to understand the influence of evaporation on the stability of a virus on a respiratory droplet. We observe the evaporation dynamics of sessile droplets from pure water and artificial saliva containing nanoparticles with similar size and structure to viruses, as well as visualize the evaporating respiratory droplets with holotomographic microscopy. To explain the acquired experimental data, a physical model is proposed by identifying a relationship between droplet evaporation and virus stability. We believe that this result would be useful to comprehend the virus stability and survivability in surfaces, allowing better safety measurements to control viral transmission through respiratory droplets.   

On Demand

We are interested in the exit time calculation for a colloidal particle present inside a sedimenting drop. This is of particular relevance to drops of saliva and mucous expelled by sneezing or coughing that could possibly contain virulent pathogens. The internal flow field of such a drop is given by the standard Hadamard-Rybczynski solution. Langevin simulations are used to calculate the mean exit time of the colloidal particle and characterize its variation with the Peclet number (Pe). In the limit of Pe<<1, the exit time is merely τ = R² / D. For the case of Pe>>1, an enhanced diffusivity is observed due to the rising prominence of the convective motion within the sedimenting drop and leads to a faster exit. We also validate the predictions from Langevin dynamics by solving a backward Kolmogorov equation for the exit-time associated with a colloidal particle in a flow field inside a sedimenting drop.