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.

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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

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Correspondence to Naiping Gao.

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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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Keywords

  • respiratory droplets
  • air distribution
  • transmission
  • airborne disease