采用CFD数值模拟技术优化发酵罐内桨叶组合

使用CFD模拟软件Fluent对实验室用7L通气搅拌发酵罐内不同桨叶组合的搅拌效果进行气液两相流模拟.首先对发酵罐自带桨叶组合进行模拟,针对模拟结果提出两种改进桨型组合,对比分析3种组合的速度矢量图、速度分布柱形图和速度云图,以此优化出一种搅拌效果较好的桨型组合.结果表明:发酵罐内的流场可受通气的影响而发生改变,通气发酵过程的模拟采用多相流模型更为准确;底层桨离底距离的不同可导致发酵罐内流场的不同,以六直叶圆盘涡轮桨为底桨时,离底距离应不小于T/3;液相死区的大小是由桨叶组合、桨叶安装位置以及气液两相的相互作用共同导致的,不能单纯靠提高转速改善;在800 r/min下,搅拌效果组合3为最佳.

Optimization of impeller combination in the aerating-fermenter with the numerical simulation method of computational fluid dynamics

The velocity field of gas-liquid fluid in a lab-scaled 7L fermenter with different impeller combinations was investigated by the commercial fluid dynamics （CFD） software Fluent in this article. Three different impeller combinations were simulated and their veloci- ty vector diagram, distribution region and contours diagram were compared. A combination with better rotation effect finally was got. The impeller and air sparger regions were described with the multiple reference（MRF） method. Result showed that the fluid field may be changed by the process of aeration in the fermenter. It is better to use the multiphase flow model in the simulation of aerobic fermen- tation process. The difference of distance between the bottom of the tank and the bottom-impeller may result in the difference of the flu- id field. The distance was no less than T/3 if the bottom-impeller was DT. The size of the fluid deadband is resulted by the difference of impeller combination, the position of impeller and the coaction of the two phases. It can not be just only improved by increasing the rotation speed individually. Under the condition of 800rpm, the combination with best rotation effect was No. 3.