Time-resolved velocity measurements using particle image velocimetry (PIV) were performed in a triple impeller stirred-tank to evaluate flow structure and flow dynamics. Using a high framing rate digital camera and a high pulse rate laser, the flow field at a planar location along the diameter of the tank was over-sampled to capture the time evolution of vortical structures in the flow. Several tests were performed for rotational speeds ranging from 175 RPM to 1575 RPM. The working fluid was glycerin at ambient conditions. Time averaged results over several blade passage cycles reveal that the vortical toroidal structure and frequency changes significantly over the RPM range investigated. A point of transition exists past which symmetry in the tank is lost, as a result of jet-jet interaction between adjacent Rushton turbines. While the flow in the region near and in between the turbines is unsteady and periodic due to blade passage, further away in the core of the mixing vessel the flow reaches a state of uniformity, as revealed from the reconstructed volumetric velocity field determined from the time-resolved PIV measurements.

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