Incipient motion of solid particles in horizontal pneumatic conveying

Abstract

A technique for finding the minimum pickup velocity of solid particles in horizontal pneumatic conveying has been developed. A general semi-empirical correlation based on the Archimedes number which is valid over a range of particle size from 10 to 1000 μm is presented for the prediction of the minimum gas velocity required to pick up particles. Experiments have been carried out with fine particles (glass beads, alumina and coal) in a 52 mm i.d. transparent pipeline. Noteworthy is the existence of a minimum point in the curves of minimum pickup velocity as a function of particle diameter for particle diameters of approximately 100 μm. Maximum conveyability is expected to occur at this particle size. Above and below this minimum point, higher gas velocities are required to pick up particles lying on the bottom of a pipe. Experiments in an actual pneumatic conveying system clarify the practical significance and usefulness of the minimum pickup velocity. Thus, it is suggested that the proposed test procedure be used as a unified technique in determining the minimum transport velocity of solid particles in horizontal pneumatic conveying systems.