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.
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Abbreviations
- C :
-
concentration (g/m3)
- C 1ε, C 2ε, C 3ε :
-
constants in the governing equation of ε
- C μ :
-
model constant ( = 0.0845)
- D :
-
particle diameter (μm)
- D p :
-
Brownian diffusivity (m2/s)
- g :
-
gravitational acceleration (m/s2)
- B G :
-
generation of turbulence kinetic energy due to buoyancy
- G k :
-
generation of turbulence kinetic energy due to the mean velocity gradients
- k :
-
turbulent kinetic energy (m2/s2)
- P :
-
pressure (Pa)
- R ε :
-
strain rate term in the ε equation
- S :
-
modulus of the mean rate-of-strain tensor
- S C :
-
source term in the concentration equation
- S ij :
-
mean rate-of-strain tensor
- S φ :
-
source term of φ
- t :
-
time (s)
- T :
-
temperature (°C)
- 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)
- V s :
-
particle settling velocity (m/s)
- w :
-
air velocity component in the z direction (m/s)
- α k :
-
the inverse effective Prandtl numbers of k equation
- α ε :
-
the inverse effective Prandtl numbers of ε equation
- β T :
-
thermal expansion coefficient (K−1)
- ε :
-
turbulent kinetic energy dissipation rate (m2/s3)
- ε p :
-
particle turbulent diffusivity (m2/s)
- φ :
-
a general scalar quantity
- μ :
-
molecular viscosity of air (g/ms)
- μ t :
-
turbulent viscosity (g/ms)
- μ eff :
-
effective viscosity (g/ms)
- ρ :
-
air density (g/m3)
- σ C :
-
turbulent Prandtl number for concentration
- σ T :
-
turbulent Prandtl number for temperature
- Γ φ :
-
general form of diffusion coefficients
References
Abadie MO, Liman K (2007). Numerical evaluation of the particle pollutant homogeneity and mixing time in a ventilated room. Building and Environment, 42: 3848–3854.
Bjorn E, Nielsen PV (2002). Dispersal of exhaled air and personal exposure in displacement ventilated rooms. Indoor Air, 12: 147–164.
Centers for Disease Control and Prevention (CDC) (1994). Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care facilities. Atlanta, GA: US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention.
Chao CYH, Wan MP, To GNS (2008). Transport and removal of expiratory droplets in hospital ward environment. Aerosol Science and Technology, 42: 377–394.
Friberg B, Friberg S, Burman LG, Lundholm R, Ostensson R (1996). Inefficiency of upward displacement operating theater ventilation. Journal of Hospital Infection, 33: 263–272.
Gadgil AJ, Lobscheid C, Adadie MO, Finlayon EU (2003). Indoor pollutant mixing time in an isothermal closed room: An investigation using CFD. Atmospheric Environment, 37: 5577–5586.
Gao NP, Niu JL (2007). Modeling particle dispersion and deposition in indoor environments. Atmospheric Environment, 41: 3862–3876.
Hinds WC (1999). Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, 2nd edn. New York: John Wiley & Sons, Inc.
Hinze JO (1975). Turbulence, 2nd edn. New York: McGraw-Hill.
Hsu DJ, Swift DL (1999). The measurement of human inhalability of ultralarge aerosols in calm air using manikins. Journal of Aerosol Science, 30: 1334–1343.
Lai ACK, Cheng YC (2007). Study of expiratory droplet dispersion and transport using a new Eulerian modeling approach. Atmospheric Environment, 41: 7473–7484.
Lai ACK, Nazaroff WW (2000) Modeling indoor particle deposition from turbulent flow onto smooth surfaces. Journal of Aerosol Science, 31: 463–476.
Li Y, Leung GM, Tang JW, Yang X, Chao CYH, Lin JZ, Lu JW, Nielsen PV, Niu J, Qian H, Sleigh AC, Su HJJ, Sundell J, Wong TW, Yuen PL (2007). Role of ventilation in airborne transmission of infectious agents in the built environment-a multidisciplinary systematic review. Indoor Air, 17: 2–18.
Morawska L, Johnson G, Ristoski Z, Hargreaves M, Mengersen K, Chao CYH, Wan MP, Li YG, Xie XJ, Katoshevshi D (2008). Droplets expelled during human expiratory activities and their origin. In: Proceedings of the 11th International Conference on Indoor Air Quality and Climate, Copenhagen, Denmark.
Nazaroff WW (2008). Inhalation intake fraction of pollutant from episodic indoor emissions. Building and Environment, 43: 269–277.
Nicas M, Nazaroff WW, Hubbard A (2005). Toward understanding the risk of secondary airborne infection: emission of respirable pathogens. Journal of Occupational and Environmental Hygiene, 2: 143–154.
Qian H, Li Y, Nielsen PV, Hyldgaard CE, Wong TW, Chwang ATY (2006). Dispersion of exhaled droplet nuclei in a two-bed hospital ward with three different ventilation systems. Indoor Air, 16: 111–128.
Sun W, Ji J, Li Y, Xie X (2007). Dispersion and settling characteristics of evaporating droplets in ventilated rooms. Building and Environment, 42: 1011–1017.
Thatcher TL, Lai ACK, Moreno-Jackson R, Sextro RG, Nazaroff WW (2002). Effects of room furnishings and air speed on particle deposition rates indoors. Atmospheric Environment, 36: 1811–1819.
Xie X, Li Y, Chwang TY, Ho PL, Seto WH (2007). How far droplets can move in indoor environments-revising the Wells evaporationfalling curve. Indoor Air, 17: 211–225.
Zhao B, Zhang Z, Li X (2005). Numerical study of the transport of droplets or particles generated by respiratory system indoors. Building and Environment, 40: 1032–1039.
Zhu S, Kato S, Yang JH (2006). Study of transport characteristics of saliva droplets produced by coughing in a calm indoor environment. Building and Environment, 41: 1691–1702.
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Gao, N., Niu, J. & Morawska, L. Distribution of respiratory droplets in enclosed environments under different air distribution methods. Build. Simul. 1, 326–335 (2008). https://doi.org/10.1007/s12273-008-8328-0
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DOI: https://doi.org/10.1007/s12273-008-8328-0