Abstract: The flow structure and shear rate in a helical ribbon stirred tank were studied employing particle image velocimetry and computational fluid dynamics in the context of simultaneous saccharification and fermentation of stover of high contents under laminar flow regime (Re<100). The effects of impeller geometry, rotational speed and rheological properties of the fluid were investigated using 11 impellers with different geometries and 5 kinds of fluid. The calculated results showed that the dimensionless angular velocity of the fluid in the core region (a) was in the range of 0.48~0.89 and decreased with the increase of impeller diameter and pitch; the dimensionless tangential, axial and radial velocities were in the ranges of 0.44~0.47, 0.06~0.09 and 0.04, respectively, the two formers decreased and increased linearly with the pitch. a decreased as the viscosity of Newtonian fluid lowered down and the shear thinning behavior of the fluid turned to be stronger. The shear rate (g) increased as the impeller diameter became smaller and the shear-thinning behavior of the fluid became significant.

Key words: biomass processing, helical ribbon, particle image velocimetry, computational fluid dynamics, flow characteristics, shear rate

摘要： 采用粒子图像测速与数值计算方法研究了螺带桨流场，选用11种几何结构桨型及5种流变性质的流体(0.3≤n≤1)，考察了层流流动(Re<100)状态下，桨叶结构、转速及流体假塑性对流型、速度分布及剪切速率分布的影响. 计算表明，核心区无量纲旋转角速度(a)随桨叶直径及螺距增大而减小，其值约在0.48~0.89；无量纲切向、轴向及径向速度分别约为0.44~0.47, 0.06~0.09及0.04，且前两者随螺距的增大分别呈线性减小及增大. a随流体粘度降低及假塑性增强而减小，非牛顿流体的流速小于牛顿流体；剪切速率随桨叶直径增大及流体假塑性增强而增大.

关键词: 生物质加工, 螺带桨, 粒子图像测速, 计算流体力学, 流动特征, 剪切速率