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° and 45° 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 Pg/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.