Study Of Flow Field In The Draft Tube Agitator Tank

Power demand and liquid circulation flux are important for appraising performance of impeller and the effect of mixing in a stirred tank. The effects of impeller type, diameter of draft-tube, clearance between draft-tube and the bottom of tank, liquid height, tube number and circulation area on the circulation flux were systematically investigated by thermo-tracing responding system in flat bottom cylindrical draft tube vessels of 0.5 m and 0.8 m in diameter. A new type of impeller was designed to generate more liquid circulation under the same power input.In this paper, the effect of draft-tube on flow field was studied in detail by using laser-Doppler velocimetry in the vessel of 0.5 m in diameter. The effects of geometry parameters of the draft tube tank on the flow field has also been analyzed. It was found that the draft-tube could enhance liquid circulation.The commercial code of CFD (Computational Fluid Dynamics), FLUENT-5, has been used to numerically simulate the flow field in the draft-tube agitated tank. It was shown that the predicted results were in qualitative agreement with the experimental data.