Prediction of Flow Characteristics and Energy Balance for a Variety of Downflow Impellers

A computational fluid dynamics (CFD) model has been developed for prediction of the flow characteristics based on the forces generated on the impeller blades. A good agreement between the CFD predictions and the experimental measurements at several locations in the vessel has been observed. The model has been validated for a wide variety of axial downflow impellers. An eddy identification scheme has been proposed to estimate the values of the turbulent length scales, eddy diffusivity, and turbulent energy dissipation rate. The impeller power number has been calculated by three methods: (i) the integration of local values of ε predicted from CFD, (ii) a method based on the forces acting on the impeller blades, and (iii) the outflow of angular momentum from the impeller zone. A good agreement has been observed between the predicted values of the power number by the previous three methods and reported values for a wide variety of axial flow impellers.