Erosion saltation

Other modes of wear are also encountered when handling slurries. As shown in Fig. 15, these include abrasion-corrosion (the most severe wear mode), scouring wear, abrasive metal-to-metal wear (crushing and grinding), high-velocity erosion, low-velocity erosion, saltation wear (rapid wear caused when particles are moved forward in a series of short intermittent bounces from a bottom surface), and cavitation. 

The lift pipe design was tapered to a larger diameter at the top. This minimized the effects of erosion and catalyst attrition, and also prevented the instantaneous total collapse of circulations when the saltation concentration, or velocity, of solids is experienced (i.e. the slump veloeity-that velocity helow which particles drop out of the flowing gas stream). In a typical operation, 2 % to 4 % eoke can he deposited on the catalyst in the reactor and burned in the regenerator. Catalyst circulation is generally not sufficient to remove all the heat of eombustion. This facilitated the need for steam or pressurized water coils to be located in the regeneration zone to remove exeess heat. 

The SDA dispersiveness in the air surface layer is determined by natural dispersiveness of soil as a source of aerosol, and by effectiveness of the sand-jet effect of saltating particles. The formation of the real size distribution of SDA in this atmospheric layer is determined by the processes of sedimentation, impingement, condensation and adsorption of gases and vapors, capture and sedimentation on obstacles and surfaces [6]. Real size distributions of soil-erosion aerosols (SEA) can be described by the power law ... 

The detachment of soil particles from bare ground, and their forward movement, increase toward the leeward side of an eroding area. On the windward side, where erosion begins and where the soil is not bombarded by bouncing particles, wind produces almost no movement of particles. This shows that the saltation process is the major one governing wind erosion without it, most soil particles would remain in place. 

Fifi, 1 5 Slurry erosion wear modes, (a) Abrasion-corrosion, (b) Scouring wear, with wear areas equal (left) and unequal (center and right), (c) Crushing and grinding, (d) High-velocity erosion, (e) Low-velocity erosion, (f) Saltation erosion, (g) Cavitation... 

Reduction of wind velocity at the fill surface and protection of facilities by strategic placement of wind screens. Given the fact that the majority of the soil movement as a result of wind erosion occurs within one metre of the ground, artificial screens, rows of natural willow twigs and/or other natural materials of limited height may be particularly useful to mitigate the saltation and creep types of soil transport. 

Much work has been carried out over the last decade concerning surface constraints on wind erosion associated with interparticle forces, inclusive of soil moisture, silt and clay, organic matter, and precipitated soluble salts. High friction velocities are required for the entrainment and transport of either very damp or aggregated particles. In the extreme case of continuous surface crusts, entrainment usually arises only through mpture from the impact of loose particles. Only a small fraction of this body of work addresses dust emission directly, while the focus has primarily been on the entrainment of sand particles and their transport via saltation. Nonetheless, since particle impact plays a key role in dust emission, such work is relevant. 

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