Risk assessment of COVID infection by respiratory droplets from cough for various ventilation scenarios inside an elevator: An OpenFOAM-based computational fluid dynamics analysis (original) (raw)
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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...
2021
We present engineering airflow to intercept the transmission of Covid19 in public spaces and public transportations, which relatively fast and simple. This technique is to suppress effectively and as massive as possible the spread of aerosols and droplets contaminated with the COVID-19 virus that is flying in the air by providing a vertical downward flow using fans placed on the ceilings and the use of floors of the certain material so that aerosol and microdroplets will not bounce back up, difficult to roll, and firmly attached to the floor. The numerical airflow simulation shows that positioning the fan on the ceiling of the room will cause the air particle to move faster downward, which will push the microdroplets to fall to the floor more quickly, so that the microdroplets and aerosols will quickly move away from the most risk organs from the transmission, namely the mouth and nose. The contactangle test results on several floor materials always show a value of fewer than 90 deg...
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...
CFD modeling of the transport of human respiratory droplets in an indoor environment
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...
Selecting the Safe Area and Finding Proper Ventilation in the Spread of the COVID-19 Virus
Energies
Coughing and sneezing are the main ways of spreading coronavirus-2019 (SARS-CoV-2). People sometimes need to work together at close distances. This study presents the results of the computational fluid dynamics (CFD) simulation of the dispersion and transport of respiratory droplets emitted by an infected person who coughs in an indoor space with an air ventilation system. The resulting information is expected to help in risk assessment and development of mitigation measures to prevent the infection spread. The turbulent flow of air in the indoor space is simulated using the k-ε model. The particle equation of motion included the drag, the Saffman lift, the Brownian force and gravity/buoyancy forces. The innovation of this study includes A: Using the Eulerian–Lagrangian CFD model for the simulation of the cough droplet dispersion. B: Assessing the infection risk by the Wells–Riley equation. C: A safer design for the ventilation system (changing the ventilation supplies and exhausts ...
Environment International, 2022
During the Covid-19 pandemic, location of the SARS-CoV-2 infected patients inside the hospital is a major issue to prevent viral cross-transmission. The objective of this study was to evaluate the risk of contamination through aerosol by using a global approach of the multiple environmental parameters to simulate, including seasonal context. A computational fluid dynamic (CFD) simulation based on the Lattice Boltzmann Method approach was used to predict airflow on the entire floor of a private hospital in Paris. The risk of contamination outside the rooms was evaluated by using a water vapor mass fraction tracker. Finally, the air contamination was estimated by a "cough model" producing several punctual emissions of contaminated air from potentially infected patients. In a winter configuration, the simulation showed a well-balanced ventilation on the floor and especially inside the rooms. After cough emissions from COVID-positive rooms, no significant contamination was observed in the circulation area, public waiting space and nurse office. On the contrary, in a summer configuration, the temperature difference due to the impact of the sun radiation between both sides of the building created additional air transport increasing the contamination risk in neighboring rooms and public spaces. Airborne spread was limited to rooms during winter conditions. On the contrary, during summer conditions, market airflow with potentially contaminated air coming from rooms located on the side of the building exposed to solar radiation was evidenced. These observations have implications to locate infected patients inside the building and for the conception of future health care structures.
ACS Omega, 2021
The airborne transmission of the COVID-19 virus has been suggested as a major mode of transmission in recent studies. In this context, we studied the spatial transmission of COVID-19 vectors in an indoor setting representative of a typical office room. Computational fluid dynamics (CFD) simulations were performed to study the airborne dispersion of particles ejected due to different respiratory mechanisms, i.e., coughing, sneezing, normal talking, and loud talking. Number concentration profiles at a distance of 2 m in front of the emitter at the ventilation rates of 4, 6, and 8 air changes per hour (ACH) were estimated for different combinations of inlet− outlet positions and emitter−receptor configurations. Apart from respiratory events, viz., coughing and sneezing characterized by higher velocity and concentration of ejected particles, normal as well as loud talking was seen to be carrying particles to the receptor for some airflow patterns in the room. This study indicates that the ″rule of thumb based safe distance approach″ cannot be a general mitigation strategy for infection control. Under some scenarios, events with a lower release rate of droplets such as talking (i.e., asymptomatic transmission) can lead to a high concentration of particles persisting for long times. For better removal, the study suggests ″air curtains″ as an appropriate approach, simultaneously highlighting the pitfalls in the ″higher ventilation rate for better removal″ strategy. The inferences for talking-induced particle transmissions are crucial considering that large populations of COVID-19-infected persons are projected to be asymptomatic transmitters.
Numerical Modeling of the Spread of Cough Saliva Droplets in a Calm Confined Space
Mathematics
The coronavirus disease 2019 (COVID-19) outbreak has altered the lives of everyone on a global scale due to its high transmission rate. In the current work, the droplet dispersion and evaporation originated by a cough at different velocities is studied. A multiphase computational fluid dynamic model based on fully coupled Eulerian–Lagrangian techniques was used. The evaporation, breakup, mass transfer, phase change, and turbulent dispersion forces of droplets were taken into account. A computational domain imitating an elevator that with two individuals inside was modeled. The results showed that all droplets smaller than 150 μm evaporate before 10 s at different heights. Smaller droplets of <30 µm evaporate quickly, and their trajectories are governed by Brownian movements. Instead, the trajectories of medium-sized droplets (30–80 µm) are under the influence of inertial forces, while bigger droplets move according to inertial and gravitational forces. Smaller droplets are locate...
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...