Gas-liquid mixing studies with multiple up- and down-pumping hydrofoil impellers: Power characteristics and mixing time

Axial flow impellers with hydrofoil blades, APV-B2, i.e., B2-30 and B2-45 (30 degrees and 45 degrees angle of attack of blades) have recently been designed, mainly for use in the up-pumping mode, and some new results are reported here for single, dual and triple impeller configurations in the turbulent flow regime. The results are compared with dual Lightnin' A-315's pumping downwards as they have traditionally been used and with dual radial flow Rushton turbines. The ungassed power numbers of the APV-B2's are low, allowing these impellers to be used at large impeller-to-tank diameter ratios. The drop in P-g/P is lower with all combinations of APV-B2 impellers, i.e., for single, dual and triple impellers when compared to other configurations tested. Torque fluctuations are less than those with single or dual down pumping axial hydrofoils. Mixing times measured using a decolourisation technique for dual and triple impeller configurations of APV-B2 under unaerated and aerated conditions showed that the mixing times are much shorter than those for the dual Rushton turbine and similar to those found for dual down-pumping A-315's. Detailed mixing characteristics and flow patterns for the dual and triple APV-B2's are also discussed.