(98c) Measurement of Wall Jets in Stirred Tanks with Varying Baffle off-Wall Clearance and Their Relationship to Solids Suspension and Cloud Height

Two-Dimensional Particle Image Velocimetry (PIV) flow measurement technique was used to measure the wall jet produced by axial pumping impeller on baffles located in an agitated vessel.  Wall Jets are the mechanism by which solids are transported from the lower region of a stirred vessel to the upper region in solids liquid mixing applications.  Baffles, width T/12, were made of transparent acrylic material with the ability to be adjusted for desired off bottom and off wall clearance. The wall jet velocity profile was measured in a 0.609m (24in.) diameter vessel, with Z/T of 1, vertically along the baffle from Z/T of 0.17 to 0.8 on both the high and low pressure side.  Data was used to test Bittorf & Kresta correlation (Bittorf & Kresta 2003) for baffles with off-wall and off bottom spacing. Cloud height was measured in a geometrically similar vessel using d80 of ~400µm silica sand particles with concentration varied between 10 and 40% by weight.  The cloud height was correlated with tip speed and different Impeller to tank diameter (D/T = 0.3, 0.4, 0.5).  Cloud height of the particle was also analyzed by comparing settling velocity of particles with jet velocity at measured cloud height.