Sedimentation factors affecting settling

Inhaled particles vary both in shape and density and these factors affect their capacity to be deposited by sedimentation. The behaviour of such particles can be determined by converting their actual diameter(s) to their aerodynamic diameters). What does this mean Imagine a low-density particle of irregular shape - this will be characterized by a certain terminal velocity as it settles in air. The aerodynamic diameter of the particle is defined as the actual diameter of a spherical particle of unit density with the same terminal velocity. 

Of these factors, the size, density, and shape of a particle are the most important determinants of settling velocity. Solids concentration and turbulence indirectly affect settling velocity by influencing formation of floes, while sediment bed roughness is a factor in deposition. Floe formation is also strongly influenced by particle and surface chemistry. Chemical properties which factor into the process of floe formation include... 

Particles (such as those present in mists, and in fumes, smokes, and dusts) present a more complex distribution pattern because the particle size affects its deposition at various levels of the airway. Such factors as sedimentation and impact rates also control particle deposition. Therefore, heavier particles may settle in the nasopharynx or upper airways, whereas lighter or smaller particles may reach more-peripheral airways. Once they have impacted, particles are susceptible to a variety of respiratory defense mechanisms. These mechanisms determine the efficiency with which particle removal progresses, thereby determining the particle s ultimate degree of adverse effects. 

Solids settling and deposition to bottom sediments is a complex process by which particulate materials, including both individual and aggregate solids, settle from the water column and adhere to the sediment bed. According to Stokes law, particle settling is dictated by particle diameter and density, but important factors causing nonideal settling include particle shape and concentration, flow velocity and turbulence, and flocculation. Deposition onto and attachment to the sediment bed are usually described as probabilistic processes, affected by turbulence at the sediment-water interface and by the cohesiveness of the solid material. 

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