Dust emission by powder handling : Comparison between numerical analysis and experimental results

The dust generation occurring during the handling of bulk materials in free falls or at the impact on a stockpile can be a source of danger for the operators health. Proper design of control systems of fugitive dust requires knowledge of the behavior of the free falling powder, the air it entrains, and the concentration of dust liberated. This paper presents first a simple model for a free falling column of bulk solids and compares it with relevant previous research. This two phase model predicts the particle and air velocities, and especially the volumetric flow of induced air in the column without dependence on any empirical constant like the entrainment constant used in the plume model. For small drop heights, the predictions of the theory appear to be in qualitative agreement with the available data for the quantity of air entrained, but the theory needs to be extended in the case of large drop heights, when the expansion of the jet of particles is large. In a second part, the description of an expanded jet of particles is experimentally studied with PIV measurements. The data obtained are well fitted by the model by Liu, when the entrainment constant is taken as the angle of expansion of the jet obtained from the velocity field.