Simulation of Airborne Transport with a Simplified Drift-Flux Model

Abstract

The use of treated wastewater for irrigation is associated with the dispersion of fine droplets containing possibly pathogens. Their inhalation could expose workers and people in the surroundings to health problems. Wind and other atmospheric conditions may increase dispersion. The risk is difficult to assess, especially with water cannons and sprinklers, whose initial droplet conditions in airborne dispersal are not well characterized. In this study, the airborne dispersion of fine droplets (smaller than 300 μm) was investigated numerically. A simplified Eulerian drift-flux model was used to obtain airborne profiles in windy conditions (between 1 and 3 m s−1), and experiments in a wind tunnel were used for validation. The model was one-way coupled, evaporation was not taken into consideration, and droplet displacement was driven by fluid drag and gravity. Two main conclusions were drawn. First, single-diameter simulations provide a qualitative evaluation of the rapidity of sedimentation but are not exhaustive to represent the entire spray. Second, more precise predictions can be obtained by introducing an approximated size distribution, resulting from a slight improvement of the initial conditions.