Modeling particle dispersion and deposition in indoor environments

Abstract

Particle dispersion and deposition in man-made enclosed environments are closely related to the well-being of occupants. The present study developed a three-dimensional drift-flux model for particle movements in turbulent indoor airflows, and combined it into Eulerian approaches. To account for the process of particle deposition at solid boundaries, a semiempirical deposition model was adopted in which the size-dependent deposition characteristics were well resolved. After validation against the experimental data in a scaled isothermal chamber and in a full-scale non-isothermal environmental chamber, the drift-flux model was used to investigate the deposition rates and human exposures to particles from two different sources with three typical ventilation systems: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). For particles originating from the supply air, a V-shaped curve of the deposition velocity variation as a function of particle size was observed. The minimum deposition appeared at 0.1-0:5 mm. For supermicron particles, the ventilation type and air exchange rate had an ignorable effect on the deposition rate. The movements of submicron particles were like tracer gases while the gravitational settling effect should be taken into account for particles larger than 2:5 mm. The temporal increment of human exposure to a step-up particle release in the supply air was determined, among many factors, by the distance between the occupant and air outlet. The larger the particle size, the lower the human exposure. For particles released from an internal heat source, the concentration stratification of small particles (diameter o10 mm) in the vertical direction appeared with DV and UFAD, and it was found the advantageous principle for gaseous pollutants that a relatively less-polluted occupied zone existed in DV and UFAD was also applicable to small particles. r

An Experimental and Numerical Study on Deposition of Bioaerosols in a Scaled Chamber

“…It is known that Staphylococcus aureus is a major multidrug-resistant pathogen that is the most prevalent cause of hospital-and community-acquired bloodstream, skin, soft tissue, and lower respiratory infections (Gandara et al 2006). An understanding of the role of ventilation in bioaerosol dispersion and deposition is essential in assessing bacteria exposure and preventing airborne infection indoors (Lai 2002;Li et al 2007;Wan and Chao 2007;Gao and Niu 2007;Zhao et al 2005;Nazaroff 2004). A drift-flux model for particle distribution and deposition in indoor environments was applied for investigation of spatial and temporal particle concentration in enclosures even the well-mixed assumption cannot hold for coarse particles (Lai and Cheng 2007).…”

CFD modelling of radioactive pollutants in a radiological laboratory

“…The approach is based on the drift-flux method described by Lai and Nazaroff [4]. In literature the drift-flux method is described extensively and the method is also specifically developed for the dispersion of particles in an indoor environment [4][5][6][7][8][9].…”

Numerical Investigation of the Wall Effect on Airborne Particle Dispersion in a Test Chamber

“…Although Gao and Niu (2007) studied the aerosol particle deposition on the walls and a nominal particle concentration on the boundary was obtained, no one investigated the effect of wall existing (including ceiling and floor) on the particle transport and distribution together with the flow field in the whole space such as the near wall region. Studies in two-phase flow showed the existing of walls can effectively influence the particle concentration in near wall region (Marchioli et al, 2003).…”

“…Some other studies focused on the indoor particle dispersion for different ventilation modes. Such as Gao and Niu (2007) used the drift-flux model to investigate the deposition rates and human exposures to particles from two different sources with three typical ventilation systems of mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD).…”