PROFILING SOLIDS FLOW FROM BINS

The bulk flow rate of particulate solids from bins and other storage vessels has been studied extensively since Ketchum's work in 1919.⁶ The flow patterns and behavior of individual particles as they approach and pass through the discharge opening, however, have received little attention. This study was undertaken to see how free flowing particles are distributed in the discharge stream from the bin, to establish something comparable to the velocity profile in a liquid flowing through a pipe.

Solids flowing by gravity through an opening in the bottom of a vessel do not move in the same way as a liquid issuing from the same opening. For one thing, solids flow at a fixed rate, virtually independent of the depth of solids in the bin, whereas liquid flow rate depends on the head. Solid particles in motion occupy more space than close-packed solids at rest; if particles are to move from a stationary bed, therefore, the solid mass must expand and the bulk density must fall. One particle must move over others on its way to the discharge opening; at the opening it separates from its fellows and drops freely away. The discharge stream consists of particles all moving at nearly the same velocity, and there is no “velocity distribution” as such; instead there is a distribution across the discharge stream of the frequency of particles passing through a given horizontal plane.