微尺度聚合物熔体的非等温平板收缩流动数值仿真

聚合物流体的收缩流动行为是微注射成型工艺过程中影响分子取向与结构的重要因素。本文采用基于有限元求解法的通用CFD软件Fidap，结合适当的边界条件，实现了微尺度条件下聚合物熔体的4：1非等温平板收缩流动的数值模拟，所用流体粘度模型为Carrcau方程，有限元单元为4节点四边形网格。结果表明，流体下游速度明显高于上游速度，速度梯度在收缩人口处明显增大，下游压力梯度大于上游压力梯度，且最大剪切速率出现在收缩人口拐点处。将仿真结果同相关文献的结果相比较发现，仿真所得聚合物流体在收缩流动过程的速度、压力及剪切速率分布规律与其在宏观尺度下的结果具有定性一致性，而温度分布则存在一定偏差。因此，宏观收缩流动仿真研究中的控制方程及本构方程仍适用于微尺度条件下流体的等温收缩流动仿真研究，对非等温微流体收缩流动行为的研究则要对能量方程做进一步修正。

Numerical Simulation for Non- Isothermal Planar Contraction Flow of Micro Scale Polymer Melt

Contraction flow behavior contributes significantly to the orientation and structure of molecular in micro injection molding. Numerical simulation of 4:1 non-isothermal planar contraction flow was realized by using CFD software based on FEM - - - Fidap with appropriate boundary condition. Carreau viscosity model andquadrangle grid with 4 nodes are employed in simulation. The results show that the velocity of downstream fluid is higher than upstream, velocity grads obviously increase in contraction entrance, and pressure grad in downstream is higher than in upstream. The highest shear rate appears in the comer of contraction entrance. Comparisons were further carried between the velocity, pressure, shear rate distribution of simulation and simulation results in macro scale from Liang zhiming etal, and the characteristic agreement of micro scale analysis results with macro scale analysis results. However, temperature distribution is different between two results. The conclusion can be drew that the control equation and constitutive equation in macro scale contraction flow simulation is still compatible with isothermal micro scale contraction flow simulation study. The energy equation must be modified in non - isothermal micro scale contraction flow behavior study.