Aerosol Transport Simulations in Indoor and Outdoor Environments using Computational Fluid Dynamics (CFD)

Abstract

This dissertation focuses on aerosol transport modeling in occupational environments and mining sites in Arizona using computational fluid dynamics (CFD). The impacts of human exposure in both environments are explored with the emphasis on turbulence, wind speed, wind direction and particle sizes. Final emissions simulations involved the digitalization process of available elevation contour plots of one of the mining sites to account for realistic topographical features. The digital elevation map (DEM) of one of the sites was imported to COMSOL MULTIPHYSICS® for subsequent turbulence and particle simulations. Simulation results that include realistic topography show considerable deviations of wind direction. Inter-element correlation results using metal and metalloid size resolved concentration data using a Micro-Orifice Uniform Deposit Impactor (MOUDI) under given wind speeds and directions provided guidance on groups of metals that coexist throughout mining activities. Groups between Fe-Mg, Cr-Fe, Al-Sc, Sc-Fe, and Mg-Al are strongly correlated for unrestricted wind directions and speeds, suggesting that the source may be of soil origin (e.g. ore and tailings); also, groups of elements where Cu is present, in the coarse fraction range, may come from mechanical action mining activities and saltation phenomenon. Besides, MOUDI data under low wind speeds (<2 m/s) and at night showed a strong correlation for particles 1-micrometer in diameter between the groups: Sc-Be-Mg, Cr-Al, Cu-Mn, Cd-Pb-Be, Cd-Cr, Cu-Pb, Pb-Cd, As-Cd-Pb. The As-Cd-Pb group correlates strongly in almost all ranges of particle sizes. When restricted low wind speeds were imposed more groups of elements are evident and this may be justified with the fact that at lower speeds particles are more likely to settle. When linking these results with CFD simulations and Pb-isotope results it is concluded that the source of elements found in association with Pb in the fine fraction come from the ore that is subsequently processed in the smelter site, whereas the source of elements associated to Pb in the coarse fraction is of different origin. CFD simulation results will not only provide realistic and quantifiable information in terms of potential deleterious effects, but also that the application of CFD represents an important contribution to actual dispersion modeling studies; therefore, Computational Fluid Dynamics can be used as a source apportionment tool to identify areas that have an effect over specific sampling points and susceptible regions under certain meteorological conditions, and these conclusions can be supported with inter-element correlation matrices and lead isotope analysis, especially since there is limited access to the mining sites. Additional results concluded that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail, provides higher number of locations with monotonic convergence than the manual grids, and requires the least computational effort. CFD simulations were approached using the k-epsilon model, with the aid of computer aided engineering software: ANSYS® and COMSOL MULTIPHYSICS®. The success of aerosol transport simulations depends on a good simulation of the turbulent flow. A lot of attention was placed on investigating and choosing the best models in terms of convergence, independence and computational effort. This dissertation also includes preliminary studies of transient discrete phase, eulerian and species transport modeling, importance of saltation of particles, information on CFD methods, and strategies for future directions that should be taken.