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Although there are some recent studies which intent to address the spread of respiratory droplets through the air, these correspond to indoor conditions or outdoor situations which not take into account realistic scenario. Less attention has been paid to the spread of respiratory droplets in outdoor environments under microclimatologic turbulent wind and which is of growing importance given the current COVID-19 epidemic. We implement a computational model describing a sneezing person in an urban scenario under a medium intensity climatological wind. Turbulence was described with a wall-modeled Large Eddy Simulation model and the spread of respiratory droplets by using a lagrangian approach. Results show the spread of respiratory droplets is characterized by the dynamics of two groups of droplets of different sizes: larger droplets (400 -900 μm) are spread between 2-5 m during 2.3 s while smaller (100 -200 μm) droplets are transported a larger range between 8-11 m by the action of the turbulent wind in 14.1 s average. Given the uncertainty of potential contagion over this way and with this reach, these efforts are an intent to contribute to shine a light on the possibility of adopting stricter self-care and distancing measures.

A three-dimensional computational model was developed to describe the coal-gasification processes inside fluidized-bed reactors. The commercial multi-purpose CFD code FLUENT 6.3 was employed, taking into account drying, volatilization, combustion and gasification processes. Both gas phase and solid phase were described using a eulerian approach to model the exchanges of mass, energy and momentum between phases. The disperse phase was described using the kinetic theory of granular flows. The chemical model involved five heterogeneous and five homogeneous chemical reactions, tracking seven species in the gas phase (CO2, CO, H2O, CH4, H2, O2 and N2) and one specie in the solid phase (C(s)). Drying and volatilization rates were estimated by mass conservation. Heterogeneous reaction-rates were determined by combining an Arrhenius kinetic-rate and a diffusion rate using the kinetics/diffusion Surface Reaction Model; the model was implemented within FLUENT through UDFs (User Defined Functions). Homogeneous reaction-rates were described by a turbulent mixing rate using the Eddy Dissipation Model available in FLUENT. Calibration and validation were performed by using existing experimental data from a benchmark coal-gasification case available in the literature. Results are in good agreement with experimental data, capturing known phenomena like fluidization-bed height, temperature distribution and species concentrations. The main contribution of the present work was implementing the necessary sub-models within the FLUENT code in order to handle reactive fluidized-beds in complex geometries. This allowed combining the flexibility of a commercial CFD code with the accuracy of simplified models developed in academic frameworks.

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