双层组合桨搅拌槽内气液微观分散特性

采用双电导电极探针法对双层组合桨搅拌槽内气液相界面积特性进行了实验研究,考察了通气量、搅拌转速和桨组合对槽内相界面积的影响。结果表明:对于上层桨为上翻斜叶桨和下层桨为凹叶桨的组合,随着通气量的增加,搅拌槽内大部分区域的相界面积增大,但在槽底区域减小。随着搅拌转速的增加,在叶轮区域的相界面积增加明显,而在槽底和液面区域基本不变化。上下层桨的分散能力和气体分布器结构和操作条件密切相关。对于近壁管式气体分布器搅拌槽,在较低通气量下,上层桨对气液分散起着主要作用,而在高通气量下,下层桨的作用增强,起主要作用。带圆盘的搅拌桨对气体具有良好的阻缓作用,不同气速下均具有优异的气液分散能力。

Local gas-liquid dispersion properties in a dual-impeller stirred vessel

The local gas-liquid interfacial area in a dual-impeller aerated vessel was measured with double-tip conductivity probes for investigating the influence of gas inlet rate,rotational speed and impeller combination on the interfacial area in the vessel. The result shows that for the impeller combination with up-pumping pitch turbine as upper impeller and concave blade turbine as lower impeller,the gas-liquid interfacial area rises with the increase of the superficial velocity in the vessel,expect for that in the bottom region. The gas-liquid interfacial area increases obviously in two impeller regions with increasing rotational speed while almost unchanged in bottom region and surface region. The gas dispersion capabilities of upper and lower impeller were affected by the structure of the sparger and operating condition. For the vessel discussed herein,at the low gas inlet rate,the upper impeller contributes more for the gas dispersion. With the increase of the gas inlet rate,the effect of the lower impeller increases and gradually shows the majority contribution to the gas dispersion. The impellers with disc can prevent the air escape from the vessel and perform good gas dispersion.