Studies of High Solidity Ratio Hydrofoil Impellers for Aerated Bioreactors. 3. Fluids of Enhanced Viscosity and Exhibiting Coalescence Repression

This paper reports on the influence of coalescence inhibition and the enhanced viscosity associated with shear thinning behavior on the fluid dynamics and power characteristics of the Prochem Maxflo T and Lightnin A315 hydrofoil impellers. The impellers, vessel, and techniques used are described in part 2 of this four‐part series of papers. Coalescence inhibition by the addition of sodium sulphate has little effect on the power drawn and by inference on the local impeller hydrodynamics although the power required to disperse gas at a given gas flow rate is reduced relative to water. The presence of shear thinning behavior and an increased viscosity (μA up to approximately 0.1 Pa s) results in a marked reduction in the ability of hydrofoil impellers to disperse gas and a reduction in the relative power drawn by the impeller. In comparison with water, the power drawn is less sensitive to operating conditions and fluid dynamic and torque instabilities are reduced for the specific geometry of a large ring sparger (DS = 0.8D) at a large absolute sparger−impeller separation.