Features of Particle Detachment by a Water Stream

Detachment of Particles in Relation to Position of Surface. The detachment 

They were mounted in a holder at two-thirds of the distance from the trough inlet, the holder being designed so that the position of the specimens relative to the flow axis could be varied. The specimens were dusted in air by free settling to a dust density of approximately 0.3 g/m. The variation in plate position that was accomplished by rotating around a vertical axis we will arbitrarily term vertical, and that accomplished by rotating around a horizontal axis we will term horizontal.  

The fraction of remaining particles with diameters of 40 and 50 fxm is approximately the same for a = 0° and a. = 180°. The fine particles with diameters of 5 and 10 jLtm are detached more poorly when ol = 180° than when a = 0°, apparently because of the specific features of flow over the dust-covered plate. The fraction of particles with a diameter of 20 jjm that remain after exposure is practically independent of the angle a in the case of the vertically positioned surfaces. The 20-jLtm particles represent a special limiting size separating the different regions in the graph for the removal of particles of different sizes depending on the position of the plate relative to the flow axis. 

Similar relationships for the 20-jum particles are observed when the slope of the plates is varied by rotating around a horizontal axis (Fig. XI.4.b). 

The removal of different fractions of polydisperse particles depends not only on the position of the plate relative to the flow direction, but also on the velocity of the water stream. As would be expected, as the water-flow velocity is increased from 0.1 to 0.5 m/sec, the fraction of remaining large particles (40-50 jLtm in diameter) decreases, and the fraction of fine particles increases. With a flow velocity of 0.85 m/sec, practically all of the adherent particles are removed. 

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