在直径0.48 m的椭圆底搅拌槽中,研究了以半椭圆管盘式涡轮(HEDT)为底桨、上两层为四叶翼型轴流桨下压操作(WHD)的组合桨(HEDT+2WHD)在搅拌槽内沿径向和轴向的局部气含率分布及不同表观气速对局部气含率的影响.局部气含率沿轴向分布比较均匀,仅在底桨附近有一个极大值,其它位置局部气含率差异较小.随着表观气速增加,沿轴向的局部气含率普遍增大,说明气量增加会强化气液分散状况.通过与HEDT+2WHU的局部气含率分布对比表明,尽管两者平均气含率接近,但组合桨下压操作时的局部气含率分布较组合桨上提操作时均匀.通过PIV方法得到两种组合桨的液相流场分布,对局部气含率分布的差别进行了解释.%In an agitator tank of 0.48 m diameter equipped with an ellipsoidal bottom cap, the vertical and radial distributions of local void fraction were measured, and the influence of superficial gas velocity on the local void fraction was studied. The triple-impeller used in the agitator tank consists of a hollow half elliptical disk turbine (HEDT) installed below and two down-pumping wide blade hydrofoils (WHD) installed above. In the stirred tank, the vertical local void fraction distributions appear evenly and the data of most locations are very close, except a maximum value of local void fraction exists near the bottom impeller. It was found that, with the increase of the superficial gas velocity, the local void fraction along the axial direction increases generally; it indicates that the increase of gas flow will strengthen the gas-liquid dispersion. Comparing with the local void fraction distribution in the agitator tank equipped with triple-impeller of HEDT+2WHu, the local void fraction distribution of HEDT+2WHD is more uniform, although both have almost the same overall gas holdups. Finally, both the averaged liquid flow fields in two agitator tanks equipped separately with HEDT+2WHD and HEDT+2WHu were measured by PIV technique, which were used to explain the differences between the two local void fraction distributions formed separately by these two different types of triple-impeller.
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