A study of an up‐ and a down‐pumping wide blade hydrofoil impeller: Part I. LDA measurements

Abstract

Abstract A wide blade, high solidity ratio, axial flow hydrofoil impeller has been developed particularly for gas dispersion when used in the upward‐pumping mode. It has a low power number so that a relatively low torque is required when using it with a large impeller to tank diameter ratio, a commonly desired aim of retrofitting. As part of the work characterising these impellers, laser Doppler anemometry has been used to study the single phase flow both down‐ and up‐pumping, the latter for the first time. Mean and root‐mean‐square velocities were measured throughout a fully baffled, flat bottomed cylindrical tank. When down‐pumping, the discharge flow was almost axial but when up‐pumping, it had a strong radial component. Turbulence energy dissipation rates in the impeller region and the discharge stream when up‐pumping were found to be higher than those when down‐pumping. In both modes, the impeller was found to have a high circulation efficiency. In Part II, the data presented here are used for obtaining computational fluid dynamic solutions of the flow field.