Hydrodynamic Characteristics of Dual-Impeller Configurations in a Multiple-Phase Stirred Tank

Experiments are carried out in a baffled flat-bottom stirred tank to test live dual-impeller configurations, including a new type of impeller, alternate blade disk turbine (ABDT). Power consumptions in gas-liquid, liquid-solid, and gas-liquid-solid systems are determined by the shaft-torque method. It is found that the configuration with all axial impeller consumes less energy than that with a radial one in all multiple-phase systems. The correlations between power input and gas flow rate or solid concentration are also discussed. Power number reaches a limit with the increase of Reynolds number in liquid-solid systems. Aeration is proved to be harmful to solid suspension. Mixing time and solid particle concentration are measured by the electric conductivity method and Powder Voidmeter PC-6, respectively. The mixing modes (axial and radial) are proposed in the light of impeller types and flow patterns. The experimental results show that the mixing time of the double radial impeller configuration is the shortest, while the double axial impeller combination performs Worst. Judging from the axial solid particle concentration distribution and overall Suspension uniformity, the combination taking pitched blade turbine downflow (PBTD) as the lower impeller achieves the best solid Suspension.