Experimental research on gas‒liquid dispersion in a stirred tank by a novel long‒short blades agitator

We used vertical short blades (SBs) and two pitched SBs with the inclined angles of the SBs from 60° to 45°, and compared the gas holdup, bubble size and interfacial area measured by the electrical conductivity probe technique when the agitator was operated in the down‒pumping and up‒pumping modes. Results show that higher gas holdup with large bubble size in the upper part and lower gas holdup but with small bubble size in the lower part of the tank. The effective fluid exchange between the radial flow generated by the long blades (LBs) and the strong axial flow generated by the SBs redistribute the bubbles effectively in the whole stirred tank. The gas phase is more evenly distributed in the whole tank with higher local gas holdup when the rotating speed is high enough. In the case of up‒pumping mode, the 45U impeller can further improve the gas‒liquid interface area. The correlation of power input and rotating speed on gas holdup is fitted.