Distribution of respiratory droplets in enclosed environments under different air distribution methods

Abstract

The dispersion characteristics of respiratory droplets are important in controlling transmission of airborne diseases indoors. This study investigates the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 − 10.0μm in an office room with three air distribution methods, specifically mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). The diffusion, gravitational settling and deposition mechanism of particulate matter were accounted by using an Eulerian modeling approach with one-way coupling. The simulation results indicate that exhaled droplets up to 10μm in diameter from normal human respiration are uniformly distributed in MV. However, they become trapped in the breathing zone by thermal stratifications in DV and UFAD, resulting in a higher droplet concentration and an increased exposure risk to other room occupants. Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV. Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone. List of symbolsin the governing equation of ε C μ model constant ( = 0.0845) D particle diameter (μm) p D Brownian diffusivity (m 2 /s) g gravitational acceleration (m/s 2 ) B G generation of turbulence kinetic energy due to buoyancy k G generation of turbulence kinetic energy due to the mean velocity gradients k turbulent kinetic energy (m 2 /s 2 ) P pressure (Pa) R ε strain rate term in the ε equation S modulus of the mean rate-of-strain tensor C S source term in the concentration equation ij S mean rate-of-strain tensor S φ source term of φ t time (s) T temperature (℃) u air velocity component in the x direction (m/s) U air velocity vector (m/s) v air velocity component in the y direction (m/s) s V particle settling velocity (m/s) w air velocity component in the z direction (m/s) k α the inverse effective Prandtl numbers of k equation Build Simul (2008) 1: 326 -335

The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

“…We used the Lagrangian approach which tracks the particle trajectory (Chao et al 2008;Gao et al 2008) and is more appropriate for the aims of our study. We treated the droplets as droplet nuclei (i.e.…”

How Many Airborne Particles Emitted from a Nurse will Reach the Breathing Zone/Body Surface of the Patient in ISO Class-5 Single-Bed Hospital Protective Environments?—A Numerical Analysis

“…Recent studies demonstrate the successful application of these two approaches in simulating airborne particle transport in similar indoor environments (Gao et al 2008;Lai and Cheng 2007;Lai et al 2008;Zhang and Chen 2007;Zhao et al 2008). For the purpose of our study, it is appropriate to use the Lagrangian approach, which tracks the particle trajectory, as shown by Chao et al (2008) and Zhao et al (2008).…”

“…Previous studies suggest that engineering simulations using computational fluid dynamics (CFD) are a valid method for investigating air flow behavior, temperature distribution and contaminant dispersion in hospital rooms using different ventilation systems (Chow and Yang 2005;Kao and Yang 2006;Cheong and Phua 2006;Qian et al 2006;Qian et al 2008;Beggs et al 2008;Chao et al 2008;RichmondBryant 2009). Further, many studies apply CFD for airborne particle transport simulations in indoor environments (Gao et al 2008;Lai and Cheng 2007;Lai et al 2008;Zhang and Chen 2007). We therefore used CFD methods to analyze the dispersion of different sized airborne particles emitted from nurses when caring for a patient in a single-bed hospital protective environment.…”

A time-based analysis of the personalized exhaust system for airborne infection control in healthcare settings

“…Many studies have proved that these respiratory droplets in normal exhaled air may carry airborne pathogens and thereby magnify the spread of certain infectious diseases (Sattar et al 1987;Papineni and Rosenthal 1997;Edwards et al 2004;Johnson and Morawska 2009). Gao et al (2008) simulated the exhaled droplets using computational fluid dynamics (CFD) by adding a 5% mass fraction of CO 2 in the exhaled air. The simulation results showed that the respiratory droplets smaller than 10.0 µm disperse like tracer gases.…”