Stirred tanks are used throughout the chemical industry for many process operations such as blending, single- or multi-phase reactions, and crystallization, to name a few. They have been the topic of much study both in academia and industry. There is still much to be understood in terms of localized dynamic phenomena such as macro-instabilities. Dynamic modeling of single phase blending in stirred tanks is of interest as a necessary first step towards understanding more complex problems such as reacting and/or multiphase flows.
To that end, turbulent blending in a stirred vessel was studied experimentally using simultaneous Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF). The experimentation was compared to computational results from Large Eddy Simulation (LES). The configuration is shown in Figure 1. The vessel is a 17.5 inch inner diameter, dish-bottomed, fully baffled tank. A nine inch diameter 45 degree pitched blade turbine (PBT) was used as the impeller, rotating sequentially at 50, 100, and 150 rpm. The impeller Reynolds numbers were 44K, 88K, and 132K, respectively. The fluorescent dye was added thru 1/8 inch tubing at a velocity of 1.36 ft/s at a distance of 6 inches above the impeller tip and 45 degrees behind the laser sheet. PIV/PLIF image data were taken at two phase-locked positions, one with the impeller blade in the plane of the laser sheet, the other 45 degrees out of plane.
LES calculations were found to be in good agreement with the measurements, as shown in Figure 2. The general features of the flowfield are consistent with those of PBT with a downward directed impeller jet stream, formation of the trailing edge vortices and high levels of turbulent kinetic energy in the trailing vortex regions.