Flow Property Measurements of Stirred-Tank Flow Across Three Reynolds Number Decades

The flow in stirred tanks is very complicated because it passes around the rotating impeller blades, interacts with the stationary baffles or stator blades leading to high-intensity turbulence, and then goes through loops and returns to the impeller region. A penetrating understanding of the flow in stirred tanks is necessary for the tank design and optimization, because it could have a significant impact to the overall design characteristics, which will affect directly the production, the quality of the product and the maintenance costs. Despite the recent advances in computational fluid dynamics (CFD), testing still plays a vital role in the development of high-performance stirred tanks. This paper describes measurements and results obtained by traversing a five-hole probe in a 6-m³ stirred tank. The three-dimensional flow field was obtained. The separation region was also detected. The majority of the measurements were conducted in the 6-m3 tank, but unique to this investigation are measurements we have conducted with Pitot tubes in an 160-m³ geometrically-similar full-scale tank. We also have earlier results obtained by Particle Image Velocimetry (PIV) in another geometrically-similar but much smaller tank, namely a 0.1m³ tank. This provides the unique opportunity to explore how such flows scale with size and speed, extending to Reynolds numbers that approach ten million. Some numerical results were also conducted, using the commercial code FLUENT, and the results are presented together with the experimental data.