The particle velocity field inside a two-dimensional aerated hopper

A two-dimensional lab-scale hopper with a flat bottom used for aeration and transparent glass front wall was used to visualize the flow pattern of fine particles (FCC particles of 64 μm and glass beads of 147 μm) near the hopper outlet at different airflow rates. Particle traces near the hopper outlet are recorded with a digital video camera and analyzed with a semiautomated image analysis procedure to yield the particle velocity field. This procedure has been verified and set up with a preliminary analysis in which the effects of several variables and in particular the frame exposure time have been addressed. Results indicate that the quality of the solids flow changes considerably with the aeration rate. At zero or low gas rates, the flow is of the funnel flow type with the formation of a well-defined channel around the hopper axis which is of the same size of the outlet. The solids on the sides are stationary. This channel widens with increasing aeration rate and solids away from the hopper axis also move. Results have been discussed and compared with pressure measurements carried out in previous work [3rd World Congress on Particle Technology (1998)].