A simplified approach for modelling airborne nanoparticules transport and diffusion

Abstract

A simplifi ed approach is proposed and used to study the TiO 2 nanoparticle transport and diffusion in an exposure chamber. This exposure chamber is used to assess lung toxicity in rats resulting from the inhalation of airborne nanoparticles. The simplifi ed approach uses computational fl uid dynamics (CFD) commercial software. The mathematical model for airfl ow is based on the three-dimensional Reynoldsaveraged Navier–Stokes equations with turbulence modeling. The mathematical model for airborne nanoparticles transport is based on assumptions such that their motions are similar to those of a singlesized diameter distribution of a passive contaminant. This model is valid as long as the nanoparticle concentration is low and the particle diameter is small enough that settling is negligible, which is the case for the exposure chamber studied. With this model, the diffusion coeffi cient is a property that plays a signifi cant role in the transport of airborne nanoparticles. The particle diffusion coeffi cient can be expressed in terms of a friction coeffi cient, and three possible relationships to model particle diffusion are presented. Their infl uences on the friction and diffusion coeffi cients are considered for the particular case of TiO 2 nanoparticles. Although all the models studied here predict a decrease in the value of the diffusion coeffi cient with increasing particle diameter, some signifi cant variations can be observed between the models. A specifi c diffusion model is selected and then used with the simplifi ed approach. The simplifi ed approach is fivalidated against available correlations for particle deposition on walls. Correlation for deposition loss rate in the case of a room agrees with numerical prediction for particle diameter between 10 and 200 nm. Particle mass concentration distribution inside the exposure chamber is also studied. The computed concentration distribution is quite uniform inside the exposure chamber and corresponds to single point measurements.