Fluid mechanics and blending in agitated tanks

A flow and mixing model can provide a sound fundamental basis for the quantitative and optimum design of impeller and tank geometries. This paper describes the results of detailed numerical simulations using such a model for the flow generated by a downflow-pitched blade turbine in a fully baffled cylindrical vessel and the subsequent bulk mixing. Comparisons of predicted flow characteristics with experimental data (measured in a 0.3 m i.d. vessel using a laser Doppler anemometer) show good agreement. The results of this flow model were then used to simulate the mixing of an inert tracer (introduced in pulse mode) in agitated tanks. Various mixing time definitions were studied and compared with published correlations. Some numerical experiments were performed to generate guidelines for the development of new impellers.