Characteristics of Free Falling Powder Jet and the Air Entrainment Phenomenon

Abstract

Characteristics of free falling powder jet of glass beads of about 450μm diameter issuing from circuler orifices of 4, 6 and 8 mm are experimentally investigated by using a laser-Doppler velocimeter in terms of axial velocity profile for several distances between 1 mm to 1500 mm from the orifice. The velocity of particles is larger than the free falling velocity of the single particle υ_tl and increases with an increase in the mass flow rate. There exists a potential like profile near the orifice. At a long distance from the orifice, the profile relative to υ_tl is similar to that of single phase free turbulent jet, while the outer part is nearly truncated by υ_tl. The spread of the powder jet is very small as compared with the single phase jet. The entrained gas flow rate by the powder jet is predicted by assuming that the particle velocity is the sum of the entrained gas velocity and υ_tl, the result being compared with previous several models.