Transport of expiratory droplets in an aircraft cabin

Linköping Electronic Conference Proceedings

For the last couple of years, the world has faced the global pandemic COVID-19. The viral transmission could occur via different modes like large respiratory droplets, direct contact with contaminated surfaces and airborne microdroplets or aerosol. This work revisits and focuses on human cough, and breathing sequence together with cough in confined spaces. We consider the Eulerian dispersion medium as a multicomponent ideal gas mixture consisting of oxygen, nitrogen and water vapor and the Lagrangian dispersed phase of human cough/breathe is modeled as pure liquid water. The unsteady complex flow is resolved with an advanced three-dimensional multiphase flow solver utilizing adaptive mesh refinement (AMR). A simplified rectangular block with a rectangular mouth area is considered to mimic human beings to inject exhaled gas and liquid droplets associated with cough and or breathing instances. The evaporation model is switched off for the particles of diameter less than 5 μm to resolv...

Building and Environment, 2020

Understanding the role of human expiratory flows on respiratory infection in ventilated environments is useful for taking appropriate interventions to minimize the infection risk. Some studies have predicted the lock-up phenomenon of exhaled flows in stratified environments; however, there is a lack of high-quality experimental data to validate the theoretical models. In addition, how thermal stratification affects the transport of exhaled particles has not been explored so far. In this study, a water tank experiment was conducted according to the similarity protocols to mimic how the expiratory airflow and particles behaved in both uniform and stratified environments. The lock-up phenomenon was visualized and compared with the predicted results by an integral model. Results showed that our previously developed theoretical model of a respiratory airflow was effective to predict the airflow dispersion in stratified environments. Stratification frequency (N) of the background fluid and the Froude Number Fr 0 of the thermal flow jointly determined the lock-up layer in a power law. For the particle dispersion, it indicated that small particles such as fine droplets and droplet nuclei would be 'locked' by indoor thermal stratification, and disperse with the thermal flow over a long distance, potentially increasing the longrange airborne infection risk. Large particles such as large droplets can deposit within a short distance, hardly affected by thermal stratification, however, droplet infection could happen to the susceptible people at a close contact with the infector. This study could give some guidance in view of cross-infection control indoors for stratified environment.

Science and Technology for the Built Environment, 2016

When infectious epidemics occur, they can be perpetuated within health care settings, potentially resulting in severe health care workforce absenteeism, morbidity, mortality, and economic losses. The ventilation system configuration of an airborne infection isolation room is one factor that can play a role in protecting health care workers from infectious patient bioaerosols. Though *

Physics of Fluids, 2022

Respiratory droplets—which may contain disease spreading virus—exhaled during speaking, coughing, or sneezing are one of the significant causes for the spread of the ongoing COVID-19 pandemic. The droplet dispersion depends on the surrounding air velocity, ambient temperature, and relative humidity. In a confined space like an elevator, the risk of transmission becomes higher when there is an infected person inside the elevator with other individuals. In this work, a numerical investigation is carried out in a three-dimensional domain resembling an elevator using OpenFoam. Three different modes of air ventilation, viz., quiescent, axial exhaust draft, and exhaust fan, have been considered to investigate the effect of ventilation on droplet transmission for two different climatic conditions (30 [Formula: see text], 50% relative humidity and 10 [Formula: see text], 90% relative humidity). The risk assessment is quantified using a risk factor based on the time-averaged droplet count pr...

Journal of Thoracic Disease, 2018

The emergence of respiratory diseases, i.e., severe acute respiratory syndrome (SARS) epidemic in 2003, H1N1 influenza epidemic in 2011 and Middle East respiratory syndrome (MERS) outbreak, reiterated the significance of ventilation in buildings. The role of ventilation in removing exhaled airborne bio-aerosols and preventing cross infections has been multidisciplinary extensively studied after the SARS outbreak in 2003. The characteristics of droplet-borne, short-range airborne and long-range airborne transmission of infectious diseases were identified. Increasing ventilation rate can effectively reduce the risk of long-range airborne transmission, while it may be of little useful in preventing the droplet-borne transmission. To maintain the airflow direction from clean cubicles to dirty cubicles is an effective way to prevent the cross infection between cubicles, which is widely used in hospital isolation rooms. Field measurements showed that wrong air flow direction was due to poor construction quality or maintenance. The impacts of different airflow patterns on removing large droplets and fine droplet nuclei were discussed. Some new concepts in general ventilation systems and local personalized equipment were also introduced. This review updates current knowledge of the airborne transmission of pathogens and the improvement of ventilation efficiency concerning the infection prevention.

2021

Respiratory droplets exhaled during speaking, coughing or sneezing have been responsible for the spread of the ongoing Covid-19 pandemic. The droplet dynamics depend on the surrounding air velocity, temperature and relative humidity. Droplets evaporate to form aerosols which contain the disease spreading virus. In a confined space like an elevator, the risk of transmission becomes higher when there is an infected person inside the elevator with other individuals. In this work, a numerical study is carried out in a 3D domain resembling an elevator using OpenFoam. Different modes of air ventilation are considered inside the elevator and the impact of these air circulations on droplet dynamics is investigated. The scenario of the opening of elevator door and the passenger leaving the elevator has also been considered in order to simulate a real life condition. A pedantic analysis of certain risk assessment factors and remedial measures to be adopted has been performed which include the...

Experimental and Computational Multiphase Flow

This study numerically investigated the transport characteristics of the cough-expelled droplets and their corresponding exposure risk of each occupant under various mixing ventilation layouts. Transient simulations were conducted in a conference room, while pathogen-bearing droplets were released by a standing speaker. The results showed that droplet residues (< 40 μm) had a high potential to reach occupant's breathing zone, among which the number fraction of aerosol residues (< 10 μm) could be nearly doubled compared with that of the rest droplet residues in the breathing zone. Occupants' exposure risks were found very sensitive to the ventilation layouts. The strong ventilated flow could significantly promote droplet dispersions when those inlets were closely located to the infectious speaker, resulting in all occupants exposed to a considerable fraction of aerosols and droplets within a given exposure time of 300 s. The mixing ventilation layout did not have a consistent performance on restricting the pathogen spread and controlling the occupant's exposure risk in an enclosed workspace. Its performance could be highly sensitive to the location of the infectious agent. Centralized vent layouts could provide relatively more consistent performance on removing droplets, whilst some local airflow recirculation with locked droplets were noticed.

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences

COVID-19 is a severe and rapidly spreading respiratory disease that can be transmitted through airborne particles, emitted from cough. This study investigated the influence of underfloor air distribution (UFAD) and overhead air distribution on the diffusion of the coughed particles emitted from two infected patients in an isolation ward. Additionally, the study examined the performance of mounting retractable covers around the exhausts on minimizing the dispersion of the particles. A coupled Eulerian-Lagrangian approach is adopted by using a discrete random walk model. The effect of Brownian force, drag force with Cunningham slip correction factor, turbulence dispersion, Rosin-Rammler, and the breakup is considered in the respiratory airborne coughed particles simulation. The model has a good agreement with the experimental data. The results show that overhead air distribution (case 1) disperses the particles faster to the occupied zone due to the strong mixing between downward inle...

Building and Environment, 2009

It has been documented that diseases can spread within an aircraft cabin from the sneezing, coughing or breathing of a sick passenger. To understand the spreading mechanism it is very important to quantify the airflow and droplet transmission around a sneezing/ coughing incident. In this project, tracer gas experiments were carried out in a full-scale Boeing 767-300 mock-up to study the global transport process of contaminated air within the cabin. Computational fluid dynamics (CFD) simulation was also used to provide additional information for understanding the principle. A steady airflow field was simulated first and then it was compared with the experimental data. The global airflow patterns were similar to those observed experimentally. This velocity field was adopted as the initial condition for further unsteady pollutant transport simulation. Experimental and simulated results were compared and discussed to develop a relationship between concentration and airflow pattern, source location, transport direction, and ventilation rate. Finally, the overall picture of concentration evolution by both experimental and simulated approaches was discussed.

Scientific Reports, 2021

The COVID-19 pandemic has generated many concerns about cross-contamination risks, particularly in hospital settings and Intensive Care Units (ICU). Virus-laden aerosols produced by infected patients can propagate throughout ventilated rooms and put medical personnel entering them at risk. Experimental results found with a schlieren optical method have shown that the air flows generated by a cough and normal breathing were modified by the oxygenation technique used, especially when using High Flow Nasal Canulae, increasing the shedding of potentially infectious airborne particles. This study also uses a 3D Computational Fluid Dynamics model based on a Lattice Boltzmann Method to simulate the air flows as well as the movement of numerous airborne particles produced by a patient’s cough within an ICU room under negative pressure. The effects of different mitigation scenarii on the amount of aerosols potentially containing SARS-CoV-2 that are extracted through the ventilation system ar...