scholarly journals Characteristics of airborne transmission under stratum ventilation

2019 ◽  
Vol 111 ◽  
pp. 02019
Author(s):  
Tao Huang ◽  
Zhengtao Ai ◽  
Arsen Melikov
Keyword(s):  
Air Distribution ◽  
Breathing Zone ◽  
Relative Positioning ◽  
Exposure Risk ◽  
Tracer Gas ◽  
Airborne Transmission ◽  
Climate Chamber ◽  
Distribution Method ◽  
Close Proximity ◽  
Droplet Nuclei

The objective of this study is to investigate the characteristics of airborne spread of exhaled droplet nuclei between two occupants in a space conditioned by a horizontal air distribution method, known as stratum ventilation. Experiments were conducted in a full-scale climate chamber. Two breathing thermal manikins were used to simulate a standing infected person and a standing exposed person, respectively. Tracer gas (N2O) was added into the air exhaled by the infected manikin. The tracer gas concentrations in the air inhaled by the exposed manikin and at the ventilation exhaust were continuously monitored. ACH was kept at 2 h-1. The variables in the experiments include the positioning of the manikins, the distance between manikins, and the room air temperature. The horizontal supply airflow to the breathing zone strongly intensifies the mixing between the flow of exhalation and the room air, which reduces the exposure risk of occupants at close proximity and flattens the risk-distance curves. The homogenization of concentration weakens considerably the importance of the relative positioning and location of the infected and exposed persons. All those characteristics of airborne transmission may not be maintained, however, if the horizontal supply jet does not interact directly with the occupants. The findings from this study are intended to contribute for better understanding of airborne transmission indoors.

scholarly journals Tracer gas is a suitable surrogate of exhaled droplet nuclei for studying airborne transmission in the built environment

2020 ◽  
Vol 13 (3) ◽  
pp. 489-496 ◽  
Author(s):  
Zhengtao Ai ◽  
Cheuk Ming Mak ◽  
Naiping Gao ◽  
Jianlei Niu
Keyword(s):  
Built Environment ◽  
Tracer Gas ◽  
Airborne Transmission ◽  
Droplet Nuclei

Measuring interpersonal transmission of expiratory droplet nuclei in close proximity

2021 ◽  
pp. 1420326X2110296
Author(s):  
Linzhi Fu ◽  
Peter V. Nielsen ◽  
Yi Wang ◽  
Li Liu
Keyword(s):  
Disease Transmission ◽  
Short Range ◽  
Close Contact ◽  
Measurement Techniques ◽  
Transmission Risk ◽  
Interpersonal Distance ◽  
Airborne Transmission ◽  
Face To Face ◽  
Close Proximity ◽  
Droplet Nuclei

Increasing evidence supports the significant role of short-range airborne transmission of viruses when in close contact with a source patient. A full-scale ventilated room (Cleanliness: ISO 14644–1 Class 5) and two face-to-face standing breathing thermal manikins were used to simulate a source individual and a susceptible person. Monodisperse particle generation and measurement techniques were used to evaluate the effect of virus-laden droplet nuclei size on short-range airborne transmission risk. We analysed four particle sizes (1.0, 1.5, 2.5, and 5.0 µm) to simulate the transport of exhaled droplet nuclei within an interpersonal distance of 0.5 m. The results indicated that the size distribution of airborne droplet nuclei could significantly influence transmission, with the inhalation fraction decreasing with increasing droplet nuclei size. Additionally, results showed that proximity to the source manikin could influence transmission. Inhalation fraction decreased with increasing interpersonal distance, fitting well with the 1/ d rule of droplet nuclei concentration decay. Our findings improve the understanding of the mechanism of the disease transmission.

scholarly journals Airborne transmission during short-term events under stratum ventilation

2019 ◽  
Vol 111 ◽  
pp. 01098
Author(s):  
Kaho Hashimoto ◽  
Zhengtao Ai ◽  
Arsen Melikov
Keyword(s):  
Steady State ◽  
Separation Distance ◽  
Control Measures ◽  
Exposure Index ◽  
Tracer Gas ◽  
Short Term ◽  
Airborne Transmission ◽  
Face To Face ◽  
Droplet Nuclei

Past studies on airborne spread of expiratory droplet nuclei between occupants were focused on long-term exposure under steady-state conditions. However, exposure during short-term events can be widely found in practice, e.g. medical examination or short meeting. Airborne transmission during short-term events under stratum ventilation was examined experimentally in this study. Two breathing thermal manikins were employed to simulate a standing infected person and a standing exposed person. The manikins were placed face-to-face and face-to-back to reproduce the exposure conditions with the highest and the lowest risk, respectively. Tracer gas was dosed into the air exhaled by the “infected” manikin to simulate the droplet nuclei. A newly developed average exposure index was used to evaluate the exposure risk. The time-averaged exposure index increases over time, but the increasing rate depends strongly on the duration of exposure time, e.g., the exposure index increases much faster during the first 5 minutes than during the period after 5 minutes. The exposure index during short-term events does not always decrease with the increase of separation distance. These findings imply that the control measures formulated based on steady-state conditions are not necessarily effective to short-term events.

scholarly journals Peering inside a cough or sneeze to explain enhanced airborne transmission under dry weather

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kai Liu ◽  
Majid Allahyari ◽  
Jorge S. Salinas ◽  
Nadim Zgheib ◽  
S. Balachandar
Keyword(s):  
High Fidelity ◽  
Substantial Variation ◽  
Ambient Conditions ◽  
Airborne Transmission ◽  
Social Distancing ◽  
Virtual Experiments ◽  
Long Time ◽  
Simulation Results ◽  
High Fidelity Simulations ◽  
Droplet Nuclei

AbstractHigh-fidelity simulations of coughs and sneezes that serve as virtual experiments are presented, and they offer an unprecedented opportunity to peer into the chaotic evolution of the resulting airborne droplet clouds. While larger droplets quickly fall-out of the cloud, smaller droplets evaporate rapidly. The non-volatiles remain airborne as droplet nuclei for a long time to be transported over long distances. The substantial variation observed between the different realizations has important social distancing implications, since probabilistic outlier-events do occur and may need to be taken into account when assessing the risk of contagion. Contrary to common expectations, we observe dry ambient conditions to increase by more than four times the number of airborne potentially virus-laden nuclei, as a result of reduced droplet fall-out through rapid evaporation. The simulation results are used to validate and calibrate a comprehensive multiphase theory, which is then used to predict the spread of airborne nuclei under a wide variety of ambient conditions.

scholarly journals DESIGNING A SMALL CLIMATE CHAMBER TO CHARACTERIZE PEOPLE AS A SOURCE OF DETERIORATION OF INDOOR AIR QUALITY BY RESPIRATION

2019 ◽  
Vol 7 ◽  
pp. 954-959 ◽  
Author(s):  
Detelin Ganchev Markov ◽  
Sergey Mijorski ◽  
Peter Stankov ◽  
Iskra Simova ◽  
Radositna A. Angelova ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Water Vapor ◽  
Air Quality ◽  
Indoor Air Quality ◽  
Indoor Air ◽  
Carbon Dioxide Concentration ◽  
Air Distribution ◽  
Vapor Concentration ◽  
Cfd Simulations ◽  
Climate Chamber

: People are one of the sources for deterioration of the indoor air quality. They worsen indoor air quality by their presence (respiration, bio-effluents), activities and habits. Through respiration, people decrease the oxygen concentration in the air of the occupied space and increase carbon dioxide and water vapor concentration in the indoor air as well as its temperature. The goal of the AIRMEN project is to find out if the rate of consumption of oxygen and emission of carbon dioxide (and water vapor) by people depends on the indoor air temperature as well as carbon dioxide concentration in the inhaled air. In order to achieve this goal a small climate chamber must be designed and constructed which allows for controlling and measuring both inflow and exposure parameters as well as for measuring outflow parameters. The principal goal of this paper is to present some important details, obtained by CFD simulations, from the design process of the climate chamber which precondition the air distribution in the chamber and hence the exposure parameters.

Experimental Study of Air Distribution Characteristics in Room of Stratum Ventilation under Two Kinds of Air Change Times

2013 ◽  
Vol 409-410 ◽  
pp. 668-672
Author(s):  
Yong Mei Xu ◽  
Jian Tang ◽  
Jun Han ◽  
Chu Qin Lin
Keyword(s):  
Experimental Study ◽  
Thermal Comfort ◽  
Experimental Studies ◽  
Air Distribution ◽  
Distribution Characteristics ◽  
Breathing Zone ◽  
Wind Speeds ◽  
Pollutant Concentrations ◽  
New Type ◽  
Better Than

Aimed at a new type of ventilation - stratum ventilation, air distributions at a breathing-zone in a model office were measured under kinds of air changes, the measure parameters in the experimental studies included temperatures, wind speeds and pollutant concentrations, based on which the thermal comfort at a breathing-zone were studied. Experimental results show that, the temperature, pollutant concentration and wind speeds in a breathing-zone under 5 times air changes are better than those under 6 times air changes. The calculating results of PMV and PPD indicate that the thermal comfort at a breathing-zone under 5 times air changes is better. The experimental study is instructive for the development of the ventilation.

Airflow Distribution and Microenvironment Evaluation of MP Task Conditioning System

2007 ◽  
Author(s):  
Guozhong Zheng ◽  
Youyin Jing ◽  
Hongxia Huang ◽  
Lijun Shi
Keyword(s):  
Numerical Simulation ◽  
Velocity Distribution ◽  
Distribution Systems ◽  
Air Distribution ◽  
Hvac System ◽  
Breathing Zone ◽  
Airflow Distribution ◽  
Air Blowing ◽  
Clean Air ◽  
Supply Velocity

During recent years an increasing amount of attention has been paid to air distribution systems with which officer can individually condition the immediate environment of their workstations. Fanger suggested supplying ventilation air that is unmixed with room air, directly to the breathing zone of each occupant. Task conditioning aims to provide each occupant with personalized clean air direct to the breathing zone. Each occupant can control the environment at his/her workplace. Microenvironment of a typical office workplace consisting of movable panel (MP) task conditioning systems was studied by numerical simulation. MP task conditioning systems were operated while a conventional HVAC system supplied air through a diffuser located in the ceiling. Air was exhausted through a ducted ceiling-level grill. Numerical simulation of 3-D turbulent flow (k-ε closure) was separately conducted to study the influence of supply velocity, air blowing distance and size of MP supply outlet on microenvironment. Three task conditioning velocities, 0.6, 0.8 and 1.0m/s, three sizes 0.3×0.15, 0.3×0.1 and 0.25×0.08m and two air blowing distances were studied. In addition to analyzing temperature and velocity distribution, Draught Rating (DR) and Predicted Percentage of Dissatisfied (PPD) of the room and workstation were studied.

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