Particles gravitational settling

Because these fog drops are much larger than the initial particles, gravitational settling is more important and acts to remove some of the particles (Pandis and Seinfeld, 1990). When the temperature rises, water begins to evaporate out of the fog droplet, concentrating the solutes. It is this process that likely led to the... 

Lawrence, M.G. Cmtzen, P.J., 1998 The Impact of Cloud Particle Gravitational Settling on Soluble Trace Gas Distributions , in Tellus, 50B 263-289. 

Other lesser mechanisms that result in aerosol removal by filters are (1) gravitational settling due to the difference in mass of the aerosol and the carrying gas, (2) thermal precipitation due to the temperature gradient between a hot gas stream and the cooler filter medium which causes the particles to be bombarded more vigorously by the gas molecules on the side away from the filter element, and (3) Brownian deposition as the particles are bombarded with gas molecules that may cause enough movement to permit the aerosol to come in contact with the filter element. Browruan motion may also cause some of the particles to miss the filter element because they are moved away from it as they pass by. For practical purposes, only the three mechanisms shown in Fig. 29-1 are normally considered for removal of aerosols from a gas stream. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

The most favorable filtration operation with cake formation is process whereby no clogging of the filter medium occurs. Such a process is observed at sufficiently high concentrations of solid particles in suspension. From a practical standpoint this concentration may conditionally be assumed to be in excess of 1% by volume. Filtration is frequently accompanied by hindered or free gravitational settling of solid particles. The relative directions of action between gravity force and filtrate... 

Sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening, i.e.. 

S. Murakami, S. Kato, S. Nagano, Y. Tanaka. Diffusion characteristics of airborne particles with gravitational settling in a convective-dominant indoor flow field. ASHRAE Transactions. 98(1), 1992, 82-97. 

For particles smaller than O.lp the random Brownian motion is greater than the motion due to gravitational settling. Therefore the above relations based on Stokes Law will not hold. 

A r Archimedes Ga pips - P)g <3 "t P- Gravitational settling of particle in fluid... 

F5 Gravitational settling of large (aeolian) particles to land 12 18... 

Americium released to the atmosphere will be associated with particulate matter and will be deposited on land or surface water by dry deposition or wet deposition (Essien et al. 1985). Dry deposition results from gravitational settling and impaction on surfaces, and wet deposition returns americium to earth in precipitation. Radionuclides resulting from atmospheric weapons tests are often injected into the lower stratosphere, while other atmospheric releases are into the troposphere. The residence time of particles in the atmosphere will depend on the altitude, latitude, season, and hemisphere because of atmospheric... 

Increasing the radius of the suspended particles, Brownian motion becomes less important and sedimentation becomes more dominant. These larger particles therefore settle gradually under gravitational forces. The basic equation describing the sedimentation of spherical, monodisperse particles in a suspension is Stokes law. It states that the velocity of sedimentation, v, can be calculated as follows ... 

Fig. 7.1 gives a size spectrum of water-borne particles. Particles with diameters less than 10 pm have been called colloids. In soils, the clay-sized and fine silt-sized particles are classified as colloids. Colloids do not dissolve, but instead remain as a solid phase in suspension. Colloids usually remain suspended because their gravitational settling is less than 10 2 cm s 1. Under simplifying conditions (spherical particles, low Reynolds numbers), Stokes law gives for the settling velocity, vs... 

Suspended particles in natural and wastewaters vary in diameter from 0.001 to about 100 pm (1 10 9 to 10 4 m). For particles smaller than 10 pm, terminal gravitational settling will be less than about 10 2 cm sec 1. The smaller particles (colloids) can become separated either by settling if they aggregate or by filtration if they attach to filter grains. 

In settling, particles of different gravitational settling velocities may collide (agglomeration by differential settling). 

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