Simulation Study on Airflow Organization and Environment in Reconstructed Fangcang Shelter Hospital Based on CFD

With frequent outbreaks of COVID-19, the rapid and effective construction of large-space buildings into Fangcang shelter hospitals has gradually become one of the effective means to control the epidemic. Reasonable design of the ventilation system of the Fangcang shelter hospital can optimize the indoor airflow organization, so that the internal environment can meet the comfort of patients and at the same time can effectively discharge pollutants, which is particularly important for the establishment of the Fangcang shelter hospital. In this paper, through the reconstruction of a large-space gymnasium, CFD software is used to simulate the living environment and pollutant emission efficiency of the reconstructed Fangcang shelter hospital in summer under different air supply temperatures, air supply heights and exhaust air volume parameters. The results show that when the air supply parameters are set to an air supply height of 4.5 m, an air supply temperature of 18 °C, and an exhaust air volume of a single bed of 150 m3/h, the thermal comfort can reach level I, and the ventilation efficiency for pollutants can reach 69.6%. In addition, the ventilation efficiency is 70.1% and 70.3% when the exhaust air volume of a single bed is continuously increased to 200 and 250 m3/h, which can no longer effectively improve the pollutant emission and will cause an uncomfortable blowing feeling to patients. © 2023 by the authors.

Large eddy simulation of sneeze plumes and particles in a poorly ventilated outdoor air condition: A case study of the University of Houston main campus.

Since the outbreak of the COVID-19 pandemic, many previous studies using computational fluid dynamics (CFD) have focused on the dynamics of air masses, which are believed to be the carriers of respiratory diseases, in enclosed indoor environments. Although outdoor air may seem to provide smaller exposure risks, it may not necessarily offer adequate ventilation that varies with different micro-climate settings. To comprehensively assess the fluid dynamics in outdoor environments and the efficiency of outdoor ventilation, we simulated the outdoor transmission of a sneeze plume in "hot spots" or areas in which the air is not quickly ventilated. We began by simulating the airflow over buildings at the University of Houston using an OpenFOAM computational fluid dynamics solver that utilized the 2019 seasonal atmospheric velocity profile from an on-site station. Next, we calculated the length of time an existing fluid is replaced by new fresh air in the domain by defining a new variable and selecting the hot spots. Finally, we conducted a large-eddy simulation of a sneeze in outdoor conditions and then simulated a sneeze plume and particles in a hot spot. The results show that fresh incoming air takes as long as 1000 s to ventilate the hot spot area in some specific regions on campus. We also found that even the slightest upward wind causes a sneeze plume to dissipate almost instantaneously at lower elevations. However, downward wind provides a stable condition for the plume, and forward wind can carry a plume even beyond six feet, the recommended social distance for preventing infection. Additionally, the simulation of sneeze droplets shows that the majority of the particles adhered to the ground or body immediately, and airborne particles can be transported more than six feet, even in a minimal amount of ambient air.

Numerical Analysis of the Impact of the Use of Personal Protective Equipment on the Face in the Process of Pollutants Spreading Emitted During Breathing

The study presents the results of a numerical analysis of the effectiveness of the use of personal protective equipment of various designs on the spread of pollutants marked with CO2 emitted during human breathing. In the study of 3D geometry the upper part of the human torso and head was developed. The simulated person was supplied with different personal protective equipment covering the human face (PPE). Two types of face shields worn at a different distance from the face and one fabric face mask was analysed. The reference geometry with no personal protective equipment was also analysed. Transient calculation with full breathing model including breath-in and breath-out and species transport were simulated. The results showed that different PPE generates different airflow patterns in the vicinity of the human face. The most efficient in reducing infection risk is by wearing a face mask or face shields at a small distance from the face, as they most effectively reduce CO2 concentration in the surrounding air. However, they also increase the re-inhalation risk of high CO2 concentration which affects human well-being.

Near-field exposure of pathogen-laden respiratory particles based on statistical evaluation of one emitting person indoors

Risk assessment models typically assume ideal mixing, in which the pathogen-laden aerosol particles emitted by a person are evenly distributed in the room. This study points out the local deviation from this idealized assumption and a correlation between the level of pathogen concentration and the distance from the emitter. For this purpose, several numerical studies (CFD) were analyzed, and a validation experiment was performed. Statistical evaluation of the spatial pathogen distribution was used to determine the potential exposure to elevated pathogen concentrations. Compared to an ideally mixed room, at a distance of 1.5 m, the mixing ventilation cases show a 25% risk of being exposed to twice the amount of pathogens and a 5% risk to more than 5 times the assumed value. For displacement ventilation there is a 75% chance of being exposed to less pathogens than in complete mixing at a distance of 1 m. The measurement values agree with the simulation results. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

SARS-CoV-2 risk assessment for a 30-minute car journey

In this paper a numerical methodology for close proximity exposure (<2m) is applied to the analysis of aerosol airborne dispersion and SARS-CoV-2 potential infection risk during short journeys in passenger cars. It consists of a three-dimensional transient Eulerian-Lagrangian numerical model coupled with a recently proposed SARS-CoV-2 emission approach, using the open-source software OpenFOAM. The numerical tool, validated by Particle Image Velocimetry (PIV), is applied to the simulation of aerosol droplets emitted by a contagious subject in a car cabin during a 30-minute journey and to the integrated risk assessment for SARS-CoV-2 for the other passengers. The effects of different geometrical and thermo-fluid-dynamic influence parameters are investigated, showing that both the position of the infected subject and the ventilation system design affect the amount of virus inhaled and the highest-risk position inside the passenger compartment. Calculated infection risk, for susceptible passengers in the car, can reach values up to 59%. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Template for Extended Abstract contributions to INDOOR AIR 2022

This investigation presents results of Computational Fluid Dynamics (CFD) modelling of aerosol behaviour within an arbitrary 'realistic' 100m2 office environment, with dynamic and variable respiratory droplet release profile applied based on published findings (Morawska et al., 2009). A multitude of ventilation strategies and configurations have been applied to the base model to compare the effectiveness of reducing the concentration of suspended aerosols over time. A key finding of the investigation indicates a relatively low sensitivity to increasing outside air percentage, and that the benefit from this strategy is heavily dependent on the in-duct droplet decay factor. The application of local recirculating air filtration systems with MERV-13 filters mounted on occupant desks proved significantly more effectiveness than increasing outside air concentration from 25% to 100% in reducing the quantity of suspended aerosols. This highlights that the ventilation industry should perhaps focus on opportunities to integrate filtration systems into furniture, partitions, cabinetry etc., and that an appliance-based solution may be more beneficial for reducing COVID-19 transmission in buildings (and likely more straightforward) than modifications to central ventilation systems, particularly in the application of refurbishments and retrofits. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Upper-Room Germicidal Ultraviolet (UR-GUV) Application in High-Ceiling Indoor Settings for Disinfection of Airborne Viruses

This study investigated upper-room germicidal ultraviolet (UR-GUV) light application in a music rehearsal room with a high ceiling (7.5 m). The focus was on the influences of the elevation and height of UV zone on disinfection of airborne viruses. This study assumed a uniform UV fluence rate of 0.2 W/m2 in the UV irradiation zone. According to the Computational Fluid Dynamics (CFD) results, average viral concentrations (Ca), fraction remaining (FR), and equivalent air exchange rate (λe) attributed to GUV, have power relationships with UV zone height. Ca and FR decreased with UV zone height, while λe did the opposite. UV zone elevation showed little influence on UR-GUV performance, indicating well-mixed air in the rehearsal room. High ceiling makes it possible to achieve adequate UV dose by increasing both UV zone height and UV light intensity. Using open fixtures improved energy efficiency and reduced operational costs of the UR-GUV system. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Evaluation of infection probability in a multiroom office space using computational fluid dynamics coupled with Wells-Riley model

The current COVID-19 pandemic has highlighted the importance of health safety assessment in various indoor scenarios. Computational fluid dynamics (CFD) combined with a modified Wells-Riley equation provides a powerful tool to analyse local infection probability in an indoor space. Compared to a single infection probability characterising the space in the traditional Wells-Riley model, the coupled approach provides a distribution of infection probability within the space. Furthermore, this approach avoids assuming a well-mixed state, usually related to Wells-Riley equation. This study compares displacement and mixing ventilation strategies with four different ventilation rates to assess the local quanta concentrations modelled using passive scalar transport approach. The simulation results are processed to also account for the effect of wearing masks and vaccinations. The result show that a well-designed displacement ventilation system can significantly reduce infection probability compared to mixing ventilation system at similar airflow rate. Additionally, the results emphasised the importance of wearing mask and getting vaccinated as a means of reducing infection probability. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Effectiveness of upper-room UVGI system in a classroom with mixing and displacement ventilation

This study investigates the effectiveness of an upper-room UVGI system in a small classroom. Mixing ventilation can increase virus removal when combined with a UVGI system more effectively than displacement ventilation combined with a UVGI system, especially in cases where the ventilation rate is low. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Gravity Settling of Particles and Ventilation Characteristics by Natural Ventilation Method

It has been suggested that COVID-19 causes airborne infection by fine particles called droplet nuclei and reducing the risk of indoor infection by ventilation is attracting attention as an infection control measure. However, the characteristics of fine particles are not considered in indoor ventilation plans, and the behavior and removal effect of particles by ventilation have not been sufficiently clarified. Therefore, in this study, numerical analysis using a single aperture model is performed under various conditions to evaluate how indoor concentration trends and ventilation rates are affected by these factors in order to properly evaluate the outflow characteristics of chemical species and particulate matter due to ventilation. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Aerodynamic performance of a ventilation system for droplet control by coughing in a hospital isolation ward.

Over 766 million people have been infected by coronavirus disease 2019 (COVID-19) in the past 3 years, resulting in 7 million deaths. The virus is primarily transmitted through droplets or aerosols produced by coughing, sneezing, and talking. A full-scale isolation ward in Wuhan Pulmonary Hospital is modeled in this work, and water droplet diffusion is simulated using computational fluid dynamics (CFD). In an isolation ward, a local exhaust ventilation system is intended to avoid cross-infection. The existence of a local exhaust system increases turbulent movement, leading to a complete breakup of the droplet cluster and improved droplet dispersion inside the ward. When the outlet negative pressure is 4.5 Pa, the number of moving droplets in the ward decreases by approximately 30% compared to the original ward. The local exhaust system could minimize the number of droplets evaporated in the ward; however, the formation of aerosols cannot be avoided. Furthermore, 60.83%, 62.04%, 61.03%, 60.22%, 62.97%, and 61.52% of droplets produced through coughing reached patients in six different scenarios. However, the local exhaust ventilation system has no apparent influence on the control of surface contamination. In this study, several suggestions with regards to the optimization of ventilation in wards and scientific evidence are provided to ensure the air quality of hospital isolation wards.

Review of Motion Simulation of Particulate Matter in the Respiratory System and Further CFD Simulations on COVID-19

Respirable particulate matter (RSP) is currently very harmful to the human body, potentially causing pulmonary silicosis, allergic rhinitis, acute bronchitis, and pulmonary heart disease. Therefore, the study of the deposition pattern of RSP in the human respiratory system is key in the prevention, treatment, and research of related diseases, whereby the main methods are computer simulation, in vitro solid models, and theoretical analysis. This paper summarizes and analyzes past deposition of RSP in the respiratory tract and also describes them in specific case studies such as COPD and COVID-19 patients, based on the review of the evidence, direction, and focus of future research focusing on simulation, experimentation, and related applications of RSP deposition in the respiratory tract. © 2023 by the authors.

Study of ozone misting for sanitization of hospital facilities: A CFD approach

The COVID-19 pandemic has demonstrated the demand for more effective procedures for sanitizing environments, especially high-risk ones, such as hospitals. Several products are used as disinfectants, with ozone being one of the strongest oxidants known. High relative humidity helps reduce the contact time required for viruses and bacteria inactivation with ozone. Thus, this work aimed to analyze the dispersion of an ozonized mist by CFD simulation to sanitize a hospital operating room. To our best knowledge, for the first time, the dispersion of an ozonized mist was investigated by CFD. The mathematical and numerical models were validated with results from the literature. The decay kinetics of the ozonized mist was obtained experimentally, resulting in a first order reaction with a kinetic constant of 2.66 × 10−4 s−1. The numerical results of concentration on the surfaces were analyzed qualitatively and quantitatively, providing relevant information about the fluid dynamics of the sanitizing process. Ozone mist concentrations were higher on the walls close to the generator and lower on the furthest walls and the ceiling. The ozone mist concentration in the room reached an average of 11 mg/L. Five minutes of ozone mist generation and another five minutes of decay by air circulation were sufficient to provide an increase in ozone mist to concentrations above 4 mg/L, considered satisfactory for the sanitization of the operating room surfaces. [ FROM AUTHOR] Copyright of Ozone: Science & Engineering is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)

A continuous flow reactor for the flexible production of different formulations: CFD-aided design

The increasing need to improve the sustainability of industrial processes requires more flexible and intensified solutions. For this purpose, nowadays lots of efforts are made to switch from batch to continuous processes, the latter being able to ensure the same processing history to all fluid elements, with a consequent better control of the operating conditions and product quality. The present work aims at developing a continuous flow reactor for the production of several fine chemicals, including medical-surgical aids, but also other substances for specific industrial sectors. The plant is basically an inline reactor equipped with various static mixers and side inlets, and it is conceived to ensure on-site production. This is an important feature also in light of the recent COVID-19 pandemic, which asked for flexible and distributed production of chemicals. Numerical simulations based on computational fluid dynamics are employed to study the performance, in terms of pressure drops and degree of mixing, of different static mixers, that is, the Lightnin Inliner Series 50 and Ross low pressure drop (LPD), combining various elements of mixing and injections in different operating conditions in both laminar and turbulent regimes. The results highlighted how numerical simulations may represent a valid tool for supporting the detailed design of such flow reactors by allowing the evaluation of the optimal design solutions.

A Numerical Study of the Effect of Limited Space Air Stability on SARS-CoV-2 Spreading in a Ventilated Room

Worldwide concern has been focused on the airborne disease of the COVID-19 pandemic. This study investigated the effect of the limited space air stability on the mechanism of SARS-CoV-2 spreading in the interpersonal breathing microenvironment using an unsteady computational fluid dynamics (CFD) method. A validated numerical model was employed to simulate the transient SARS-CoV-2 releasing process from normal breathing activity. The computational domain was divided into an interpersonal breathing microenvironment and the rest macroenvironment. A displacement ventilation system was implemented with 1.5 ACH, 3 ACH, 7.4 ACH and 9 ACH. Two standing CSPs (Computational Simulated Person) were placed in the middle of the macroenvironment face-to-face with a relative distance of 1 m. Simulation results indicated that in stable cases, the exhaled SARS-CoV-2 tended to accumulate in the interpersonal breathing microenvironment and resulted in a relatively high infection risk for people;whereas in cases where unstable air presented, SARS-CoV-2 concentration was significantly reduced. The unstable conditions lowered the risk of person-to-person transmission in confined spaces. Also, it was found that unstable cases performed better in energy efficiency in comparison with the stable conditions.

Aerosol transmission in queuing and dining scenarios in canteens and the effectiveness of control measures

This study investigates the aerosol transmission in queuing and dining scenarios in canteens and explores the effectiveness of control measures. An improved Wells-Riley equation is adopted to calculate the infection risk. The dilution of exhaled aerosols is difficult in the crowded queuing scenario, where the replacement of queuing positions increases the cross-infection risk. The highest infection risk is 1.16% and 1.08% for the linear-queue and cross-queue condition, respectively. Shortening the queuing duration, increasing the separation distance, and wearing masks can considerably reduce the infection risk. In the dining scenario, the effect of increasing ACH is limited on reducing the local concentration. An exhaust vent installed close to the top of the partition can effectively remove the local high-concentration aerosols. Intermittent occupation of a seat can considerably reduce the transmission risk between the consecutive dinners taking that seat. These findings should contribute to improved control of infectious transmission in canteens.

Numerical simulation of social distancing of preventing airborne transmission in open space with lateral wind direction, taking into account temperature of human body and floor surface.

This paper presents the numerical results of particle propagation in open space, taking into account the temperature of the human body and the surface of the ground. And also, the settling of particles or droplets under the action of gravitational force and transport in the open air is taken into account, taking into account the temperature during the process of breathing and sneezing or coughing. The temperature of the body and the surface of the ground, different rates of particle emission from the mouth, such as breathing and coughing or sneezing, are numerically investigated. The effect of temperature, cross-inlet wind, and the velocity of particle ejection from a person's mouth on social distancing is being investigated using a numerical calculation. The variable temperature of the human body forms a thermal plume, which affects the increase in the trajectory of the particle propagation, taking into account the lateral air flow. The thermal plume affects the particles in the breathing zone and spreads the particles over long distances in the direction of the airflow. The result of this work shows that in open space, taking into account the temperature of the body and the surface of the ground, a 2-m social distance may be insufficient for the process of sneezing and social distance must be observed depending on the breathing mode.

The airflow distribution and aerosol diffusion rules in the negative pressure isolation ward

Negative pressure wards are significant in preventing the spread of infectious pathogens which play a crucial role in fighting against COVID-19. Owing to the negative pressure, contaminated air with pathogens is not able to flow from the wards to non-contaminated zones while fresh filtered air will be transported to the ward via the ventilation system. As airflow controlled by ventilation systems affects the motion of pathogens, for example, infectious aerosol particles, the ability of a negative pressure ward to reduce the risk of infection highly relies on an effective ventilation system. In this investigation, impacts of airflow patterns under various human postures and ventilation processes aerosols diffusion are analyzed via the computational fluid dynamics (CFD) simulation. According to the results, among three airflow patterns, the highest contaminant removal efficiency is 57% at 200 s with the top supply and bottom return mode;besides, in three postures, in the case that the patient is in a standing position, the contaminant removal efficiency is the highest. Furthermore, it is found that the best airflow scheme is a slit tuyere in the ward, with a top supply and side return mode and a sitting position for the patient. This study may provide a reference for the design of airflow in negative pressure isolation wards, control of contaminants, and prevention of viral infections, so as to ensure a good working and recovery environment for medical staff and patients. [ FROM AUTHOR] Copyright of Simulation is the property of Sage Publications, Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)

A novel slip-velocity model to simulate the filtration performance of nanofiber media.

Aerosols such as PM2.5 and PM10 can have an immense impact on human health. With the outbreak of SARS-CoV-2, it is urgent to filter aerosols by media filtration technology. Electrospun nanofibers are a promising material for achieving high efficiency, low resistance, light weight, and environmentally friendly air filtration. But research on filtration theory and computer simulation of nanofiber media is still lacking. The traditional method involving computational fluid dynamics (CFD) and Maxwell's first-order slip boundary overestimates the slip velocity on the fiber surface. In this study, a new modified slip boundary was proposed, which introduced a slip velocity coefficient on the basis of the no-slip boundary to address the slip wall. Our simulation results were compared with the experimental pressure drop and particle capture efficiency of real polyacrylonitrile (PAN) nanofiber media. The computational accuracy on pressure drop of the modified slip boundary improved 24.6% and 11.2% compared with that of the no-slip boundary and Maxwell's first-order slip boundary, respectively. It was found that the particle capture efficiency near the most-penetrating particle size (MPPS) was significantly increased when slip effect occurred. This may be explained by the slip velocity on the fiber surface, which would make particles more accessible to the fiber surface and captured by interception.

Displacement ventilation to avoid COVID-19 transmission through offices.

Respiratory infections such as COVID-19 can be spread by respiratory droplets with a diameter larger than 5-10 µ m or by droplet nuclei with a diameter smaller than 5 µ m . Besides wearing masks, fresh air should be supplied frequently in closed rooms to avoid infections. Constructing and operating new isolation rooms require time, money, and maintenance cost, which are scarce in the current pandemic and in many communities. Displacement ventilation may be a feasible and secure option in temporary hospitals and other buildings to control the disease. This paper investigates using CFD simulations how displacement ventilation systems can deliver high air quality, and thermal comfort and minimize the risk of COVID-19 infection in enclosed spaces.