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

The characteristics of a free falling powder jet of glass beads are investi gated in terms of axial velocity profile at several distances ranging betwe en 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 th at of the single particle in an unbounded fluid v(s) and increases with inc reasing mass flow rate. A uniform profile exists near the orifice. At a lon g distance from the orifice, the velocity profiles of powder jet are like t hose 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 slight ly greater than v(s). The diffusion of the powder jet is very small as comp ared with that of a single-phase jet. (C) 2001 Elsevier Science B.V. All ri ghts reserved.