Experimental and computational investigation of the laminar flow structure in a stirred tank

The laminar flow structure inside an unbaffled stirred tank generated by a 6-blade radial flow impeller was characterized using flow visualization experiments, particle imaging velocimetry (PIV) experiments, and computational fluid dynamics (CFD) simulations. As expected from a previous study (Lamberto et al., 1996), the dominant flow structures in the system were two ring vortices above and below the impeller. These secondary circulation regions were segregated from the bulk of the flow and, for low impeller Reynolds numbers (5 < Re < 100), their positions and size were found to depend on Re and on the position of the impeller blades. The pumping capacity and circulation flow of the impeller were quantified and results indicate that the circulation flow was approximately 4 times the pumping capacity of the impeller.