螺带-螺杆搅拌槽内流动与剪切特性的数值模拟

Numerical Simulation of Flow and Shear Characteristics in Helical Ribbon-Screw Impeller Stirred Tanks

以高黏物系混合为背景,采用数值模拟方法,选用高黏强剪切稀化流体为研究对象,考察了桨叶几何结构对螺带-螺杆搅拌槽内的流场及剪切特性的影响,研究内容包括流场精细结构(轴向速度及剪切速率分布)及搅拌槽宏观特性参数(轴向循环流量及体积平均剪切速率).计算发现,对搅拌槽内轴向速度影响最为显著的几何结构参数为螺带宽度(w_(HR)),随着w_(HR)/d_(HR)由0.05增大至0.20,最大向下无量纲轴向速度(u_z/u_(tip))_(maxD)由0.09增大至0.34;w_(HR)/d_(HR)=0.13时,搅拌槽内轴向循环流量Qz达到最大;搅拌槽内剪切速率与桨叶宽度及直径成正比,与螺距成反比;壁区影响最为敏感的为桨叶直径;s_(HR)/d_(HR)=0.4时,搅拌槽内体积平均剪切速率最高.最后,综合考虑搅拌槽内流场及剪切特性的几何效应,给出了螺带-螺杆搅拌桨设计建议.

The flow and shear characteristics in helical ribbon-screw impeller stirred tank were investigated numerically and the influence of the geometrical parameters was given in the mixing of high viscous and highly shear-shinning liquid. The detailed flow structure （axial velocity and shear strain profile） and macro mixing parameters of the stirred tank （axial circulation rate and volumetric average shear strain rate） were given. It was found that the impeller width （wHR） had the most obvious effect on the liquid axial velocity. The downward maximum dimensionless axial velocity （uz/uip）maxD increased from 0. 09 to 0. 34 and the axial circulation rate （Qz） reached maximum at WHR/dHR=0. 13. The shear strain rate was proportional to WHR and dnR, and was inversely proportional to SHR. The volume average shear strain rate of the wall region （7 k） was most sensitive to impeller diameter and that of the tank （γav）Was highest at SHR/dHR= 0. 4. Considering the effect of geometry on the flow and shear characteristics, suggestions of the design parameters of the impeller were provided.