Characterization and modeling of a high-pressure water-fogging system for grain dust control

Grain dust, a health and safety risk, is generated whenever grain is loaded into or unloaded from hoppers and equipment. This research investigated airflow models and evaluated the particle dynamics from a high-pressure water-fogging system for potential dust control at a grain-receiving hopper. Experiments were performed in a test chamber, representing a narrow section of a grain-receiving hopper. A 0.2 mm (0.008 in.) spray nozzle was used to produce a plume of fog directed across a free-falling grain column. More than 90% of the fog droplets ranged from 10 to 40 μm in diameter. Average droplet velocities in the plume cross-section were over 10 m s^-1 at 7.6 cm from the nozzle. The air-velocity pressures at 7.6 cm were parabolic in the radial direction, with maximum pressures over 275 Pa (1.1 in. H₂O). Airflow distributions, grain dust transport, and spray droplet trajectories within the test chamber were modeled in three dimensions using FLUENT, which is a computational fluid dynamics (CFD) software program. Induced airflow from the spray fog caused recirculation of the air and dust particles in the lower part of the chamber. This recirculation pattern transported the dust from the grain pile back into the spray plume, where it mixed with the spray fog. The spray produced deposits on the surface of the grain pile ranging from 0.1 to 0.4 mg cm^-2 s^-1. However, when the grain pile filled the chamber and was positioned directly in the spray plume, the grain surface deposits were 1.2 mg cm^-2 s^-1 at the grain peak. The spray produced deposits on the sidewall of the chamber. Sidewall spray deposits were 11 mg cm^-2 min^-1 in the middle of the test chamber and 1.5 mg cm^-2 min^-1 near the outlet. The sidewall dust deposits during spray treatment ranged from 1.2 to 0.5 mg cm^-2 min^-1 and correlated with the spray deposits with an R² of 0.95.