基于CFD多螺杆反应器挤出特性的分析

利用ANSYS/FLOTRAN 程序对聚乙烯熔体在双螺杆、一字型三螺杆、三角形三螺杆和四螺杆反应器中的流动进行了分析, 对三角形三螺杆和四螺杆反应器中流道的中心区进行了重点研究, 并对4 种类型反应器的挤出特性进行了比较。结果表明, 螺杆反应器的啮合区具有较大的速度梯度, 有利于物料的充分混合。双螺杆、一字型三螺杆、三角形三螺杆和四螺杆反应器的啮合区个数分别为1, 2, 3, 4 个, 由于啮合区个数的增加, 其物料混合能力也逐渐增强。三角形三螺杆和四螺杆反应器具有特殊的结构“中心区” 。中心区的物料形成环流, 环流的存在促进了中心区物料的混合, 增加了物料在中心区的混合时间;经过计算, 物料不能滞留于中心区。双螺杆、一字型三螺杆、三角形三螺杆和四螺杆反应器的流量、回流量、回流系数以及平均剪切速率依次逐渐增大。从理论上验证了多螺杆反应器在物料输运能力以及物料混合能力等方面均具有较佳的能力, 多螺杆反应器更适合聚合物的加工。

Extrusion Characteristic's Analysis of Multiple-Screw Reactors Based on CFD

The flow of melt polyethylene in double-screw extruder,"—"-shaped tri-screw extruder,triangular tri-screw extruder and four-screw extruder was analyzed by means of ANSYS/FLOTRAN.The special study focused on the central area of reactor's flow path of triangular tri-screw extruder and four-screw extruder. Extrusion characteristic of four types of reactors was compared.The results show that a large velocity gradient emerges in the intermeshing region of the screw reactors,which is helpful to mix materials sufficiently.The four reactors have different numbers of intermeshing regions.Double-screw reactor,"—"-shaped tri-screw extruder,triangular tri-screw extruder and four-screw extruder have one,two,three,and four intermeshing regions respectively.With the increase of the number of intermeshing regions,the mixing ability of materials is enhanced gradually.Triangular tri-screw extruder and four-screw extruder have special structure,that is,central region.Materials in the central region form circumfluence,which promotes the mixing effect and prolongs the mixing time of materials in the central region.Through calculation,the materials cannot be hold up in the central area.For double-screw extruder,"—"-shaped tri-screw extruder, triangular tri-screw extruder and four-screw extruder,flow rate,back flow rate,coefficient of back flow rate and average rate of shear are incremental gradually.It is verified in theory that the multiple-screw extruders have good material transportation and mixed ability.Multiple-screw extruder is fitter for polymer processing.