Experimental investigation of a free falling powder jet and the air entrainment

The characteristics of a free falling powder jet of glass beads are investigated in terms of axial velocity profile at several distances ranging between 1 to 1500 mm from different orifices using a laser-Doppler velocimeter. The free falling velocity of a particle in the powder jet is larger than that of the single particle in an unbounded fluid vs and increases with increasing mass flow rate. A uniform profile exists near the orifice. At a long distance from the orifice, the velocity profiles of powder jet are like those of a single-phase free turbulent jet, provided that the outer edge of the powder jet does not extend past the radius where the velocity is slightly greater than vs. The diffusion of the powder jet is very small as compared with that of a single-phase jet.