Mixing Characteristics under Gas Injection through Rotary Lance Submerged in Liquid Bath

The mixing time of a water bath stirred by gas injecton through a rotary lance was measured by an electrical conductivity method. Effects of the gas flow rate, the rotation speed and the bath depth on the mixing time were examined. Measurement of torque produced during the lance rotation was also carried out. It is found that the effect of the gas flow rate on the mixing time becomes significant in the deep bath, H, under the low rotation speed, R. In the present experiments, the conditions are H/D>0.625 and R <0.33 s⁻¹, where D is the vessel diameter. On the other hand, the effect of the lance rotation is appreciable when the bath is shallow. The torque increases with increasing the rotation speed, whereas the bath depth has no effect on the torque. The results are explained in terms of specific powers of the injected gas and the rotary lance. The effects of operating variables on the mixing time are examined quantitatively from the multiple regression analysis.