偏心转子挤出机中UHMWPE熔体流动特性的数值模拟

偏心转子挤出机具有良好的正位移输送特性，能有效解决超高分子量聚乙烯（UHMWPE）由于壁面滑移造成的加工困难的问题。为了揭示UHMWPE在偏心转子挤出机输送段的熔体流动特性，采用实验与数值模拟相结合的方法确定了UHMWPE熔体壁面滑移的模型参数，利用ANSYS Polyflow软件对UHMWPE熔体的流场进行了数值模拟。结果表明：偏心转子挤出机中转子和定子啮合形成的容腔能够实现对UHMWPE熔体的正位移输送，容腔截面尺寸的变化在熔体中产生了拉伸流场；在每个容腔的入口和出口附近分别形成正压和负压，啮合间隙不为0时，造成容腔中熔体的逆流和漏流，使容腔出口处的平均流率低于理论流率。偏心转子挤出机加工UHMWPE时，容腔出口处熔体的瞬时流率和平均流率与转子转速成正比，流率脉动率保持不变；减小转子和定子间的啮合间隙，容腔出口处熔体的平均流率增加，流率脉动率减小，增强了偏心转子挤出机中熔体的正位移输运。

Numerical Simulation on Melt Flow Characteristics of UHMWPE in Eccentric Rotor Extruder

The processing difficulties of UHMWPE caused by the wall slip can be solved effectively by the eccentric rotor extruder, which make the melt conveyed in positive displacement. To reveal the melt flow characteristics of UHMWPE in the conveying section of the eccentric rotor extruder, the model parameters of wall slip were determined by the combination of experiment and numerical simulation, and the flow field of UHMWPE melt was numerically simulated by ANSYS Polyflow. The results show that the UHMWPE melt in the cavity formed by the meshing of the rotor and the stator can be conveyed in positive displacement, and the change in the cross-sectional size of the cavity leads to the elongation flow field in the melt. When the meshing gap exists, the positive pressure and negative pressure formed around every inlet and outlet respectively, will lead to the counterflow and leakage of the melt in the cavity and make the average flow rate at the outlet of the cavity lower than the theoretical flow rate. When UHMWPE is processed by the eccentric rotor extruder, the instantaneous flow rate and average flow rate of the melt at the outlet of the cavity are proportional to the rotor rotation speed, while the pulsation rate of the flow rate remains unchanged. Reducing the meshing gap between the rotor and the stator increases the average flow rate of the melt at the outlet of the cavity and decreases the pulsation rate of the flow rate, which enhances the positive displacement conveying of the melt in the eccentric rotor extruder.