Comparison of Power Number for Paddle Type Impellers by Three Methods

Abstract

Power numbers in a baffled stirred tank with paddle type impellers were measured over a range of Reynolds numbers from laminar to turbulent flow. Impellers include two-blade flat paddle impeller, 45° two-blade pitched paddle impeller, pitched blade turbine (PBT, 45° four-blade) and double-stage pitched blade turbine, with impeller-to-tank diameter ratio of 0.5-0.6. The measured power numbers were compared with other two methods, the prediction by using correlations and Computational Fluid Dynamics (CFD). Power number correlations showed that the estimated values from the empirical correlation of Nagata (1975) close agreed with the measured ones in the laminar region, the deviation was large in the transitional and turbulent regions. The power numbers from the correlation of Kamei et al. (1996) and Hiraoka et al. (1997) got good agreement from laminar to turbulent regions. The power number in stirred tank was also simulated by CFD method. The numerical results showed satisfactory agreement with the experimental data over a wide range of Reynolds numbers.