反向旋转卧式双轴捏合反应器混合特性的数值模拟

Numerical simulation of mixing process in different opposite-rotating horizontal twin-shaft kneaders

以差速反向旋转卧式双轴捏合反应器为研究对象,选用高黏牛顿流体糖浆为模拟物料,通过三维有限元数值模拟方法研究了高黏糖浆在捏合反应器中的流动过程,获取了流速和剪切速率的空间分布,进一步结合粒子示踪技术探究了分布混合过程与混合效率,并且考察了搅拌结构对流动与混合过程的影响规律。研究表明,捏合反应器中几乎不存在流动死区,桨叶末端和重叠区域的流速和剪切速率较高,且高流速和高剪切区域均随着捏合杆数目和捏合杆长度的增加而增大。捏合杆可以推动物料在圆周方向上的运动,在重叠区域存在周期性交互作用,进而可以强化分布混合过程。拉伸率随着混合时间以指数形式增加,且随着捏合杆数目和捏合杆长度的增加而增加。时均混合效率大于零,随着捏合杆数目的增大而增大,随着捏合杆长度的增加呈现先增大后减小的趋势。

The finite element method(FEM)was adopted to study the hydrodynamics in the horizontal opposite rotating twin-shaft kneader with different rotating speeds in a highly viscous Newtonian fluid syrup solution.The particle tracking technique was used to investigate the mixing process.The effect of kneader configuration on hydrodynamics and mixing process was analyzed.Studies have shown that there is almost no dead zone in the kneading reactor,and the flow velocity and shear rate at the end of the blade and the overlapping area are high.And the high flow velocity and high shear area increase with the increase of the number of kneading bars and the length of the kneading bars.The kneading bars,pushing material points into the angular position,periodically intermesh in the overlapping zone.Hence,the distributive mixing process in the kneader can be greatly enhanced.The length of stretch exponentially increases with time and with the increasing of the number and length of kneading bars.The time averaged mixing efficiency remains positive during the mixing process,which increases with the number of kneading bars.When the length of kneading bars increases,the time averaged mixing efficiency tends to increase in the beginning and then decrease.