Coagulation gravitational

Aerosols are solid or liquid particles, suspended in the liquid state, that have stability to gravitational separation over a period of observation. Slow coagulation by Brownian motion is implied. 

Gases and grains in interstellar clouds probably experienced many shock events during the formation of planetesimals and meteorites. These events are as follows 1) coagulation of dust into clumps, which settle to the equatorial plane of the nebula 2) breakup of the gravitationally unstable dust disk into clusters of dust clumps 3) coalescence of the clusters into 1 km planetesimals ... 

Mass fractal dimension is able to determine the extent of gravitational coagulation and sedimentation that take place as the particles traverse the airway. 

Aerosol particles used for inhalation deposit within the lower respiratory tract mainly by inertial impaction, sedimentation, and diffusion. Loose fractal aerosols were found to settle slower and therefore had more time to increase gravitational coagulation with other floes leading to much more rapid particle growth. This will increase the chance of the aerosol floes settling on the airway walls before reaching the end of the airways. 

The molecules of both HSl and HS2 have a high colloid stability due to their very low collision efficiency and small size which prevent them from settling under normal gravitational acceleration. Their separation in a centrifuge with a g value of some thousands is still practically inefficient. This fact is used for sedimentation analysis to investigate the destabilization and aggregation rate of the coagulation process of humic substances. 

Figure 4. Residence time of particles in seconds (left axis) and days (right axis) as a function of particle radius. The shaded areas represent estimates of the lifetimes made as follows 1, molecular or ionic clusters C, coagulation of particles P, removal by precipitation F, gravitational settling A, derived from spatial distribution of Aitken particles R, derived from the distribution of small radioactive particles. From Kreidenweis et al. (1999) in Atmospheric Chemistry and Global Change by Brassem et al. 1999 by Oxford University Press, Inc. Used by permission.

This division is very convenient from the point of view of particle characterization and measurement. Thus, in the range of Aitken particles diffusion effects are significant and particle coagulation is rapid. However, in case of giant particles these phenomena can be neglected and the behaviour of aerosol particles is mostly determined by their sedimentation due to gravitation. The large particles constitute... 

Aerosol particles below the cloud base are captured by precipitation elements due to gravitational coagulation. This type of coagulation is caused by the difference between falling speeds of the aerosol particles and the raindrops or snow crystals. In other words, this means that precipitation elements overtake the particles. The air molecules go around the falling drops (or crystals) while large particles are impacted against the drops due to their inertia. For this reason precipitation elements are considered to be small impactors (see Subsection 4.1.2). 

Aerosol particles suspended in a fluid may come into contact because of their Brownian motion or as a result of their motion produced by hydrodynamic, electrical, gravitational, or other forces. Brownian coagulation is often referred to as thermal coagulation. 

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