Respirable dust presents as a severe health threat to workers in industries as diverse as coal mining, metal and nonmetal mining, metal fabrication, metallurgy, and construction. In China, for example, over 20,000 workers per year have been diagnosed with pneumoconiosis since 2010 due to the excessive exposure to dust. Laudable efforts have been directed towards minimising workers' inhalation of respirable dust.

Driven by their small size and the humid environment, dust particles tend to stick together to form aggregates, which have been recognised as fractal objects that possess self-similar structures. Compared to individual particles, the motion of fractal aggregates is much more difficult to quantify due to their intricate structure, inherent non-uniformity in primary particle size and density, and complex interaction with fluid flow. The understanding of the aerodynamics of fractal aggregates is way incomplete. This, in turn, hinders the development and commercial deployment of conventional or emerging dust removal technologies.

This study examines the morphological and aerodynamic characteristics of fractal dust aggregates. Specifically, aggregation of primary dust particles is simulated using the discrete element method (DEM). The morphological characteristics of the formed aggregates are described in terms of fractal dimension, coordination number and gyration radius. Subsequently, the dust aggregate is released in the air and let it settle and reach its steady state; the settling is solved using a fully coupled lattice Boltzmann method (LBM) and DEM. The slow aggregation process leads to a compact structure of dust aggregates. When reaching their steady settling state, aggregates tend to orientate with their maximum projection area perpendicular to the falling direction. The dependency relationship between the aerodynamics of dust aggregates and their morphological characteristics is established.        

Respirable dust, dust aggregates, fractal, aerodynamics,LBM-DEM,dust removal