General trends of gravity separation

Ascending turbulent two-phase currents are a frequent phenomenon in natural and industrial situations alike. They are exceedingly complex. Attempts to describe the processes involved by analytic means have not met with success. It has been seeking to elucidate the principal mechanisms operating in two-phase flow by examining natural finely dispersed materials moving in channels of varying shape, length and configuration. Visual observation supported by filming reveals that the process is totally chaotic. The motion of each particle is purely random, i. e., it is impossible to predict either the instantaneous velocity of motion of a given particle or the direction of this velocity. Nevertheless, it is possible to formulate a clear-cut physical law that fully characterizes the process under consideration. It has been found that in every concrete case there exists a range of velocities within which the solid phase of the stream is distributed between the upper and lower outlets according to a fixed relationship. The law, it has been formulated and validated experimentally for this range of velocities, is that separation of the various narrow size classes (between the two ends of the channel) proceeds in an identical manner regardless of its configuration and length. This uniformity reflects the invariance of the phenomenon with respect to the size composition of the solid phase, the size and density of the particles, and the velocity and density of the carrier medium. It has been verified for an array of powdered materials of diverse densities in 87 different channels.