不同组合桨搅拌槽内非牛顿流体的微观混合特性

Micro-mixing characteristics of non-Newtonian fluid in a stirred tank agitated with different impellers

在直径0.282m的搅拌槽内,以羟乙基纤维素(HEC)水溶液为工作体系,以磷酸盐-碘化物-碘酸盐平行竞争反应为模型反应,比较了非牛顿流体体系中向心桨、Rushton桨、三斜叶桨的功率准数,考察了加料时间、桨型及双层桨组合对微观混合效果的影响。结果表明,随功率增大,功率准数基本不变,Rushton桨功率准数最大,是向心桨的两倍、斜叶桨的四倍。随加料时间增大,离集指数先减小后不变。在实验考察范围内,单位体积功耗相等的情况下,单层桨微观混合效果的顺序为Rushton桨>向心桨>斜叶桨,双层桨中高剪切的Rushton桨与强循环的斜叶桨组合的微观混合效率最高。

In order to investigate the micro-mixing performance of centripetal turbine in a non-Newtonian fluid system,the parallel competitive reactions of phosphate/iodide/iodate were used to measure the segregation index in a 0.282 m diameter cylindrical oval-bottom baffled stirred tank.The micro-mixing performance was compared among standard six straight blade turbine(DT),down-pumping pitched blade turbine(PBTD),centripetal turbine(CT),and ten dual-impeller combinations.The power numbers of single impellers were measured experimentally.And the influences of injection time,power consumption of unit volume,impeller type on the segregation index were investigated.The results showed that the power number remained constant with the increase of power,and the power number of DT was roughly twice that of CT and four times of PBTD.With the increase of feeding time,the segregation index decreased gradually to an asymptotic level.With the increase of power consumption per unit volume,the segregation index of the three propellers decreased gradually,and keeps the relative level of DT< CT<PBTD.For the dual-impellers systems,the product distribution was dominated by the upper impeller since the feeding location was at the liquid surface.It was found that the combination of PBTD and DT with both strong shear and intensive circulation was more advantageous among the dual-impeller systems.In the dual CTs with backswept installation of lower propeller enhanced the micro-mixing.Contrast between single and double impellers at the same power consumption per unit volume,most of dual-impeller systems can improve the micro-mixing due to complementary flow pattern.