The above-mentioned gas–liquid–solid systems are the cases of heavier particles (settling in liquid phase) suspended in liquids. The mixing of gas–liquid floating particles is another branch of three-phase systems and is also encountered in process
industries. However, little attention has been devoted to the liquid-phase mixing time in gas–liquid-floating particles three- phase systems. Xu et al. (2000) investigated the effects of impeller type, baffles, gas sparger, rotational speed, gas volumetric flow rate and particle fraction on mixing time in multi-impeller three- phase gas–liquid-floating particle systems by measuring tem- perature differences using thermocouples. Their work revealed that the axial flow was the most important factor for the liquid phase mixing time. Liquid phase mixing time in other three-phase systems is scarcely investigated, and practically no report on the mixing time in gas–liquid–liquid agitated reactors has been found in the open literature, in spite of its importance. The purpose of this paper is to contribute to the knowledge on the macro-mixing of the continuous phase in the simultaneous presence of both gas and oil as dispersed phases, particularly to explore the effect of aeration and the dispersed oil phase on macro-mixing in the continuous phase. The mixing time and power consumption in both liquid–liquid and gas–liquid–liquid systems are measured. The effects of various operation conditions on the macro-mixing of liquid phase are analyzed and the mixing time data are correlated.