Global and local gas−liquid characteristics (gas hold-up, volumetric mass transfer coefficient), and flow field, mixing time of the liquid phase are investigated for various triple-impeller configurations. Four types of impellers (Rushton turbine (RT), hollow blade turbine (HBT), wide-blade hydrofoil impeller pumping down (WHd), and pumping up (WHu)) were used to form four combinations (3RT, HBT+2WHd, HBT+2WHu, and 3WHu). The results show that the axial impellers combination (3WHu) provides more effective homogenization performance than the impellers with combined radial and axial flow (HBT+2WHu, HBT+2WHd), while the radial impellers combination (3RT) is the worst. When the gas superficial velocity is 1.625 mm s −1 , 3WHu produces a 53% higher mass transfer coefficient than HBT+2WHd, HBT+2WHu, and 3RT lie between them. When the gas superficial velocity reaches up to 8.124 mm s −1 , however, all of the tested configurations give almost similar mass transfer coefficients under equivalent power input. For 3RT, the highest hold-up is in the bottom impeller discharge stream and near the wall for the middle and top impellers. For the HBT+2WHd combination, there was no large variations of gas hold up in the bulk except the region around the bottom impeller. For HBT+2WHu and 3WHu, high gas hold-up was observed between the two up pumping impellers, and moderately low gas hold-up above the top impeller. There are three zones of higher interfacial area for the HBT +2WHu and 3RT combination, two zones of higher interfacial area for 3WHu, and only one zone of higher interfacial area for HBT+2WHd combination. At low gas velocity, the flow pattern generated by each impeller combination results in different gas bubble trajectory and different bubble breakup and coalescence kinetics, which in turn influences both local and average gas holdup directly, and also affects the local specific interfacial area, that is, influences the mass transfer coefficient indirectly. At higher gas velocity, the power drop also contributes to change of the gas hold-up and mass transfer at the same specific power consumption.

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In this article, computational investigation of the gas-liquid ow in stirred tank with multiple Rushton impellers was carried out. Experimental results of average and local details of gas-liquid ow characters were reported, including gas-holdup, bubble Sauter diameter, speci c area and mass transfer coe cient. Thoroughly interphase momentum transfer models including drag and non-drag models were investigated, together with four mass transfer coe cient models using commercial CFD software ANSYS CFX 12.0. Among the drag models tested, the modi ed Brucato model showed more accurate results than others, while non-drag models showed slight e ects on the average ow and local ow characters. For accurate local ow simulation, the population balance model (PBM) showed quite sensitive e ect on the local gas distribution. Simulation of interphase mass transfer with eddy cell model showed the most agreement with experimental measured data. Additionally, two advection schemes were employed and compared with each other to test their ability to get more accurate simulation result.

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