幂律流体在Kenics型静态混合器中流动特性分析

为了探究Kenics型静态混合器内扭旋叶片剪切作用对幂律流体流动的影响，利用旋转流变仪测量了浓度为0.5wt%, 0.7wt%, 0.9wt%的羧甲基纤维素(CMC)水溶液的流变参数，采用数值模拟与实验研究了扭旋叶片作用下幂律流体流动阻力和剪切稀化特性。对流场研究表明，扭旋叶片诱导产生了内流涡旋、绕流涡旋和近壁面涡旋，有效强化了静态混合器内流体流动的剪切作用。受多个纵向涡旋分布的影响，扭旋叶片局域流场中周向45°位置速度最高，周向30°位置涡量与剪切应力最高而黏度最低。径向0.4倍半径位置速度最高，0.7倍半径位置黏度最高。静态混合器有效提高了流体的二次流流动速度和剪切应力，降低了幂律流体的黏度和流动阻力系数。

Analysis of flow characteristics of power law-fluid in Kenics static mixer

The purpose of this work is to explore the flow of power-law fluid in Kenics static mixer. The flow was affected by the element shearing action of Kenics static mixer. Discovery HR-2 rheometer was used to measure the consistency coefficient K and rheological index n of the carboxymethyl cellulose solution at 0.5wt%, 0.7wt% and 0.9wt%. The parameter of power-law fluid was provided for the numerical simulation. The computational fluid dynamics software Fluent was used to simulate the computational domain. The flow resistance and shear-thinning characteristic in the Kenics static mixer were experimentally measured and numerically simulated in the conditions of the element aspect ratio Ar=1.0~2.0 and the flow rate 50×10-6~450×10-6 m3/s. It was showed that the resistance coefficient of the twisted blade with Ar=2.0 was 66.6% lower and the viscosity was 9.0% higher than that with Ar=1.0. The flow research showed that the internal-flow vortex, the detour-flow vortex and the near-wall vortices were induced by twist blade. The formation and dissipation of near-wall vortices played a good role in drag reduction because the internal vorticity and shear stress were increased and the viscosity of carboxymethyl cellulose solution was effectively reduced. The longitudinal vortices enhanced the shear effect of fluid flow in the static mixer. Affected by the vortices, the highest velocity was at 45° of circumferential direction in the local flow field of the element. The highest vorticity, shear stress and the lowest viscosity were at 30° of circumferential direction. The velocity was the highest at 0.4 times radius and the viscosity was highest at 0.7 times radius. The secondary flow velocity and shear stress were improved effectively by Kenics static mixer, and the viscosity of power-law was reduced. The flow resistance coefficient was effectively reduced with the flow velocity increasing, the power-law fluid concentrations reducing and the element aspect ratio reducing. The study about flow characteristics of a power-law fluid in Kenics static mixer provided the basic data for optimizing structure design.