Carbon dioxide(CO_(2))is often monitored as a convenient yardstick for indoor air safety,yet its ability to stand in for pathogen-laden aerosols has never been settled.To probe the question,we reproduced an open-plan ...Carbon dioxide(CO_(2))is often monitored as a convenient yardstick for indoor air safety,yet its ability to stand in for pathogen-laden aerosols has never been settled.To probe the question,we reproduced an open-plan office at full scale(7.2m×5.2m×2.8m)and introduced a breathing plume that carried 4% CO_(2),together with a polydisperse aerosol spanning 0.5–10μm(1320 particles s^(−1)).Inlet air was supplied at 0.7,1.4,and 2.1 m s^(−1),and the resulting fields were simulated with a Realisable k–εRANS model coupled to Lagrangian particle tracking.Nine strategically placed probes provided validation;the calibrated solution deviated fromthe experiment by 58 ppm for CO_(2)(8.1%RMSE)and 0.008 m s^(−1)for velocity(15.7%RMSE).Despite this agreement,gas and particles behaved in sharply different ways.Room-averaged CO_(2)varied by<15%,whereas the aerosol mass rose to almost three-fold the background within slowmoving corner vortices.Sub-micron particles stayed aloft along streamlines,while those≥5μmpeeled away and settled on nearby surfaces.The divergence shows that neither the CO_(2)level nor themeanageof air,taken in isolation,delineates all high-exposure zones.We therefore recommend that ventilation design be informed by a composite diagnosis that couples gas data,size-resolved particle measurements,and rapid CFD appraisal.展开更多
A computational fluid dynamic （ CFD ） analysis of air movement and aerosol particle transport in a two-zone ventilated room with an inter-zonal opening is presented to study the impact of ventilation strategies and ...A computational fluid dynamic （ CFD ） analysis of air movement and aerosol particle transport in a two-zone ventilated room with an inter-zonal opening is presented to study the impact of ventilation strategies and size of the opening on indoor particle dispersion and concentration distribution. The comparisons of average particle concentrations in both zones between the computations and the experiments from the literature are generally satisfactory and acceptable. The combined effects of sizes of the opening and the inlet and outlet locations （three different strategies） are simulated and discussed. The results show that ventilation strategy and size of the opening influence the particle removal rate in zone 1. The removal rate is decreased when the air supply system is changed from the tap-inlet to the bottom-inlet configuration. The top-inlet system obtains a better particle deposition in zone I than the bottom-inlet configuration. However, the particle concentration at breathing level is lower for bottomsupply system than for top-supply. Decreasing the size of interzonal opening increases the particle deposition rate in zone 1 only for the top.supply system, especially for coarse particles.展开更多
A demand for renewable alternatives that would be able to deal with the problems related to well-being is directly linked to the world’s growing needs to save energy and reduce environmental costs. For a project impl...A demand for renewable alternatives that would be able to deal with the problems related to well-being is directly linked to the world’s growing needs to save energy and reduce environmental costs. For a project implementation addressing these issues, it is essential to know the climatic conditions of the target area. Taking natural ventilation, climatic factors, and renewable alternatives as important sources of comfort, in this work, passive strategies, through the utilization of microclimate elements as well as the location of outside obstacles, were imposed on an initial and specific project. The objective was to introduce obstacles which could interfere in the field of external wind and evaluate whether this outside intervention is able to make changes in indoor air circulation. The wind fields for the studied cases were obtained by computational simulations, and their consequences were analyzed to attain thermal comfort. The method adopted to obtain the wind fields was a Petrov-Galerkin type method, which is a stabilized mixed finite element method of the Navier-Stokes equations considering the incompressibility and formulated in primitive variables, velocity and pressure. The obtained results point to the solutions that promote the increase or decrease of the wind-field intensity.展开更多
Ventilation strategies in patients with severe tracheal stenosis should be tailored to the patient according to the underlying cause and narrowing location.This report is on a case of a 68-year-old male patient,who wa...Ventilation strategies in patients with severe tracheal stenosis should be tailored to the patient according to the underlying cause and narrowing location.This report is on a case of a 68-year-old male patient,who was admitted for radiotherapy because of esophageal cancer and then developed severe stenosis at the cervical trachea.We used venovenous extracorporeal membrane oxygenation to secure the airway and ensure adequate oxygenation.Then urgent endoscopic balloon dilation of airway stenosis was successfully performed under general anesthesia.This case shows that venovenous extracorporeal membrane oxygenation can be used in endoscopic tracheal procedures for patients with severe benign stenosis in the upper-trachea who are unable to tolerate conventional ventilation.展开更多
Mechanical ventilation(MV)is an important strategy for improving the survival of patients with respiratory failure.However,MV is associated with aggravation of lung injury,with ventilator-induced lung injury(VILI)beco...Mechanical ventilation(MV)is an important strategy for improving the survival of patients with respiratory failure.However,MV is associated with aggravation of lung injury,with ventilator-induced lung injury(VILI)becoming a major concern.Thus,ventilation protection strategies have been developed to minimize complications from MV,with the goal of relieving excessive breathing workload,improving gas exchange,and minimizing VILI.By opting for lower tidal volumes,clinicians seek to strike a balance between providing adequate ventilation to support gas exchange and preventing overdistension of the alveoli,which can contribute to lung injury.Additionally,other factors play a role in optimizing lung protection during MV,including adequate positive end-expiratory pressure levels,to maintain alveolar recruitment and prevent atelectasis as well as careful consideration of plateau pressures to avoid excessive stress on the lung parenchyma.展开更多
People in elevators are at risk of respiratory infection because the elevator cabin is crowded and has poor ventilation.The exhaled particles may be inhaled by the susceptible person,deposited on the surface and suspe...People in elevators are at risk of respiratory infection because the elevator cabin is crowded and has poor ventilation.The exhaled particles may be inhaled by the susceptible person,deposited on the surface and suspended in the elevator,which can result in direct and indirect transmission.However,whether the air vent designs adopted in the elevator can effectively reduce the transmission risk of respiratory particles remains unknown.In this study,the dispersion of particles under four common ventilation strategies used in the commercial elevator was investigated by proven computational fluid dynamics(CFD)simulations.The flow field was simulated with the RNG κ-ξ turbulence model and the Lagrangian method was adopted to track particle trajectories.The effects of air vent layout and airflow rate on particle transmission were analyzed.We found that more than 50% of exhaled particles(average value)were suspended in the cabin and difficult to discharge under the investigated ventilation strategies.The deposited fraction of particles on the susceptible person reached up to 39.14% for infiltration ventilation,which led to a high risk of contact infection.Increasing the ventilation rate could not significantly reduce the inhalation proportion of particles due to the poor airflow distribution inside the elevator.A more proper ventilation strategy should be explored for the elevator to control transmission risk.展开更多
Elevators,as an enclosed and often crowded space,pose a high risk of airborne infections due to ineffective ventilation.To mitigate this issue,this study introduces a reinforced exhaust at low velocity(RELV)system,spe...Elevators,as an enclosed and often crowded space,pose a high risk of airborne infections due to ineffective ventilation.To mitigate this issue,this study introduces a reinforced exhaust at low velocity(RELV)system,specifically designed to enhance aerosol removal efficiency in elevators.The performance of the RELV system was assessed through computational fluid dynamics(CFD)simulations,employing the Renormalization Group(RNG)k–εturbulence model to simulate airflow and the Lagrangian method to track particle motion.The RELV system was benchmarked against three conventional ventilation strategies:mixed ventilation(MV),displacement ventilation(DV),and local exhaust(Exhaust).Results demonstrated that the RELV system,optimized at a momentum ratio of 0.2,achieved a remarkable 72.9% aerosol removal efficiency within 120 s,significantly outperforming the 16.1%removal efficiency of the MV system under Scenario I,where the patient was located at the elevator’s center.Furthermore,the viral aerosol concentration in the breathing zone was reduced from 2.03×10^(-2) mg/cm^(3) in the MV system to 1.02×10^(-3) mg/cm^(3) in the RELV system.The RELV system features simple design and compatibility with existing ventilation systems,offering an effective solution to improve air quality in elevators and other enclosed environments.Additionally,this study provides a velocity decay curve for low-velocity jets in the RELV system.This curve offers valuable insights for designing ventilation systems in similar settings.展开更多
文摘Carbon dioxide(CO_(2))is often monitored as a convenient yardstick for indoor air safety,yet its ability to stand in for pathogen-laden aerosols has never been settled.To probe the question,we reproduced an open-plan office at full scale(7.2m×5.2m×2.8m)and introduced a breathing plume that carried 4% CO_(2),together with a polydisperse aerosol spanning 0.5–10μm(1320 particles s^(−1)).Inlet air was supplied at 0.7,1.4,and 2.1 m s^(−1),and the resulting fields were simulated with a Realisable k–εRANS model coupled to Lagrangian particle tracking.Nine strategically placed probes provided validation;the calibrated solution deviated fromthe experiment by 58 ppm for CO_(2)(8.1%RMSE)and 0.008 m s^(−1)for velocity(15.7%RMSE).Despite this agreement,gas and particles behaved in sharply different ways.Room-averaged CO_(2)varied by<15%,whereas the aerosol mass rose to almost three-fold the background within slowmoving corner vortices.Sub-micron particles stayed aloft along streamlines,while those≥5μmpeeled away and settled on nearby surfaces.The divergence shows that neither the CO_(2)level nor themeanageof air,taken in isolation,delineates all high-exposure zones.We therefore recommend that ventilation design be informed by a composite diagnosis that couples gas data,size-resolved particle measurements,and rapid CFD appraisal.
基金National Natural Science Foundation of China (No.40975012)
文摘A computational fluid dynamic （ CFD ） analysis of air movement and aerosol particle transport in a two-zone ventilated room with an inter-zonal opening is presented to study the impact of ventilation strategies and size of the opening on indoor particle dispersion and concentration distribution. The comparisons of average particle concentrations in both zones between the computations and the experiments from the literature are generally satisfactory and acceptable. The combined effects of sizes of the opening and the inlet and outlet locations （three different strategies） are simulated and discussed. The results show that ventilation strategy and size of the opening influence the particle removal rate in zone 1. The removal rate is decreased when the air supply system is changed from the tap-inlet to the bottom-inlet configuration. The top-inlet system obtains a better particle deposition in zone I than the bottom-inlet configuration. However, the particle concentration at breathing level is lower for bottomsupply system than for top-supply. Decreasing the size of interzonal opening increases the particle deposition rate in zone 1 only for the top.supply system, especially for coarse particles.
基金the FAPERJ(State of Rio de Janeiro research supporting foundation)
文摘A demand for renewable alternatives that would be able to deal with the problems related to well-being is directly linked to the world’s growing needs to save energy and reduce environmental costs. For a project implementation addressing these issues, it is essential to know the climatic conditions of the target area. Taking natural ventilation, climatic factors, and renewable alternatives as important sources of comfort, in this work, passive strategies, through the utilization of microclimate elements as well as the location of outside obstacles, were imposed on an initial and specific project. The objective was to introduce obstacles which could interfere in the field of external wind and evaluate whether this outside intervention is able to make changes in indoor air circulation. The wind fields for the studied cases were obtained by computational simulations, and their consequences were analyzed to attain thermal comfort. The method adopted to obtain the wind fields was a Petrov-Galerkin type method, which is a stabilized mixed finite element method of the Navier-Stokes equations considering the incompressibility and formulated in primitive variables, velocity and pressure. The obtained results point to the solutions that promote the increase or decrease of the wind-field intensity.
基金the Science Technology Department of Zhejiang Province(LGF19H010010)the Health and Family Planning Commission of Zhejiang Province(2020KY156).
文摘Ventilation strategies in patients with severe tracheal stenosis should be tailored to the patient according to the underlying cause and narrowing location.This report is on a case of a 68-year-old male patient,who was admitted for radiotherapy because of esophageal cancer and then developed severe stenosis at the cervical trachea.We used venovenous extracorporeal membrane oxygenation to secure the airway and ensure adequate oxygenation.Then urgent endoscopic balloon dilation of airway stenosis was successfully performed under general anesthesia.This case shows that venovenous extracorporeal membrane oxygenation can be used in endoscopic tracheal procedures for patients with severe benign stenosis in the upper-trachea who are unable to tolerate conventional ventilation.
文摘Mechanical ventilation(MV)is an important strategy for improving the survival of patients with respiratory failure.However,MV is associated with aggravation of lung injury,with ventilator-induced lung injury(VILI)becoming a major concern.Thus,ventilation protection strategies have been developed to minimize complications from MV,with the goal of relieving excessive breathing workload,improving gas exchange,and minimizing VILI.By opting for lower tidal volumes,clinicians seek to strike a balance between providing adequate ventilation to support gas exchange and preventing overdistension of the alveoli,which can contribute to lung injury.Additionally,other factors play a role in optimizing lung protection during MV,including adequate positive end-expiratory pressure levels,to maintain alveolar recruitment and prevent atelectasis as well as careful consideration of plateau pressures to avoid excessive stress on the lung parenchyma.
基金supported by the Shandong Provincial Natural Science Foundation,China(No.ZR2021QE027).
文摘People in elevators are at risk of respiratory infection because the elevator cabin is crowded and has poor ventilation.The exhaled particles may be inhaled by the susceptible person,deposited on the surface and suspended in the elevator,which can result in direct and indirect transmission.However,whether the air vent designs adopted in the elevator can effectively reduce the transmission risk of respiratory particles remains unknown.In this study,the dispersion of particles under four common ventilation strategies used in the commercial elevator was investigated by proven computational fluid dynamics(CFD)simulations.The flow field was simulated with the RNG κ-ξ turbulence model and the Lagrangian method was adopted to track particle trajectories.The effects of air vent layout and airflow rate on particle transmission were analyzed.We found that more than 50% of exhaled particles(average value)were suspended in the cabin and difficult to discharge under the investigated ventilation strategies.The deposited fraction of particles on the susceptible person reached up to 39.14% for infiltration ventilation,which led to a high risk of contact infection.Increasing the ventilation rate could not significantly reduce the inhalation proportion of particles due to the poor airflow distribution inside the elevator.A more proper ventilation strategy should be explored for the elevator to control transmission risk.
基金supported by the National Key R&D Program of the Ministry of Science and Technology,China,on“National Quality Infrastructure(NQI)”(Grant No.2023YFF0613101)the National Natural Science Foundation of China(NSFC)through Grant No.52108084.
文摘Elevators,as an enclosed and often crowded space,pose a high risk of airborne infections due to ineffective ventilation.To mitigate this issue,this study introduces a reinforced exhaust at low velocity(RELV)system,specifically designed to enhance aerosol removal efficiency in elevators.The performance of the RELV system was assessed through computational fluid dynamics(CFD)simulations,employing the Renormalization Group(RNG)k–εturbulence model to simulate airflow and the Lagrangian method to track particle motion.The RELV system was benchmarked against three conventional ventilation strategies:mixed ventilation(MV),displacement ventilation(DV),and local exhaust(Exhaust).Results demonstrated that the RELV system,optimized at a momentum ratio of 0.2,achieved a remarkable 72.9% aerosol removal efficiency within 120 s,significantly outperforming the 16.1%removal efficiency of the MV system under Scenario I,where the patient was located at the elevator’s center.Furthermore,the viral aerosol concentration in the breathing zone was reduced from 2.03×10^(-2) mg/cm^(3) in the MV system to 1.02×10^(-3) mg/cm^(3) in the RELV system.The RELV system features simple design and compatibility with existing ventilation systems,offering an effective solution to improve air quality in elevators and other enclosed environments.Additionally,this study provides a velocity decay curve for low-velocity jets in the RELV system.This curve offers valuable insights for designing ventilation systems in similar settings.
