大型侧进式搅拌釜内湍流流场的数值模拟

Numerical simulation of turbulent flow field in industrial-scale side-entering stirred tank

采用计算流体力学(CFD)技术对直径和高度均为13 m的大型侧进式搅拌釜内均相宏观流场进行数值计算。结果表明,将计算域划分为大约90万网格时,计算得到的搅拌功率曲线与实验数据吻合较好;考察不同操作转速、搅拌桨安装角度及个数对釜内低速死区分布的影响,发现增大搅拌转速很难有效地消除水平面上的死区;搅拌桨垂直向下5.71°或水平偏转11°安装能明显改善流体运动。三桨和四桨搅拌体系对釜上部流场的优化要好于两桨体系;但在相同转速下,双桨、三桨和四桨搅拌釜的搅拌功耗分别是单桨搅拌釜的1.2倍、2.3倍和3.4倍。综合考虑,三桨体系搅拌效率较高。最后采用组分模型计算得到不同转速下三桨釜的混合时间。

Computational Fluid dynamics （CFD） technique was employed to simulate the single-phase turbulent flow field in an industrial-scale stirred tank equipped with a side-entering impeller. The calculated power curve and velocity profiles were in good agreement with the available experimental results for the finer-mesh cases with 900,000 grids in the calculation domain. The effect of impeller rotation speed and impeller layout on the mixing effect was studied. The results indicate that the increasing of impeller speed can not effectively eliminate the low- velocity dead zones, and the flow pattern can be obviously improved when the impeller is inserted into the tank with a vertical angle of 5.71° or a horizontal angle of 11°. Compared with two-impeller stirred system, the three-and four-impeller systems can more obviously decrease the area of low-velocity dead zones, especially in the top part of the tank. But the total power consumption of two-, three- and four-impeller stirred tank is 1.2, 2.3 and 3.4 times that of the single-impeller stirred tank. The mixing time of a three-impeller stirred tank under the different impeller speeds was calculated by using species model.