Flow and Heat Transfer Characteristics of High-Polymer Flow with Free Gas-Liquid Interface Boundary

工业上应用的高分子材料（注塑等）在熔融和连续相变过程中，其流场和传热场的若干特征行为取决于其非牛顿性质和非线性温度依赖关系。在材料加工过程中，这些流动和热行为对保持和控制工程质量变得越来越重要。熔融聚合物实验研究的难点主要在于没有合适的实验方法可以同时高精度地测量非定常流动和换热场，从而检测出具有时效性的非牛顿特性及其非定常效应。在本研究中，采用可视化图像和多点非定常测量相结合的数值层析成像技术，对具有自由气液界面边界的高分子流体熔体前缘的非定常流动和换热现象进行了实验研究。从连续视频图像中检测到对整个换热场有重要影响的气液界面的地理形状和速度矢量场，通过换热传感器检测到流体到壁面的换热情况。首先在室温条件下用液态高聚物（PEO）进行了预试验，以验证方法的正确性，然后在与实际工程材料加工基本相同的条件下进行了多次试验。将高分子材料（PP）放入具有许多实心原短棒的圆柱形管中。在管道中，由于电加热器和摩擦热的作用，温度上升到材料的熔点以上，材料在运输过程中发生了相向的变化。在可控步进电机的驱动下，活塞将熔化液在表面张力的作用下从喷嘴中推出到管状和矩形通道中。将出口速度条件改为被推活塞的运动速度，以明确其作用。利用CCD摄像机进行多图像处理，实验检测了熔锋的连续三维形状和再附着。并尝试从随时间分离的两幅图像中提取速度矢量和剪应力分量来检测熔体前缘的流场。从实验结果中，我们发现了以下几个有趣的现象：在近壁面矢量图上，气液界面的形状随速度波动而随时间变化，这意味着在分子水平上存在几种局部和不均匀的滑动现象。熔体前缘的热传递也发生了变化，并与这一现象相关。这些源于高聚物性质的现象，有助于建立传热机理模型，以明确所有现象，并用数值模拟来估计熔化的整个过程。少

In the melting and continuous phase changing of the high-polymer material on industrial applications (injection molding and etc.), there are several characteristic behaviors in the flow field and heat transfer field in depends on its non-newtonian properties and non-liner temperature dependencies. These flow and heat behaviors become more important recently to keep and control engineering quality in the material proctessing. The difficulty of the experimental investigation of the melting high-polymer is mainly that there is no appropriate experimental method to measure the unsteady flow and heat transfer field simultaneously with high accuracy that can detect the time-special non-newtonian properties and its unsteady effects.In this study, the unsteady flow and heat transfer phenomena in melt-front of high-polymer fluid with free gas-liquid interface boundary will be shown experimentally with a numerical tomography by visualization images and multi-point unsteady measurements. The unst … More eady geographic shape of the gas-liquid interface and velocity vector field in melt-front which make important effects on whole heat and transfer field, are detected from the continuos images by video, and heat transfer from fluid into wall detected by the heat transfer sensors. The pre-experiments using liquid high-polymer (PEO) with a room temperature were done at first for checking methods, and then several experimental trials have done with mostly same conditions as real engineering material processing. The high-polymer materials (PP) were put into the cylindrical tube with many solid original short bars. In the tube, as the temperature raise over melting point of material by electric heaters and frictional heat generation, the material change its phase aspect in transit. The melting fluid with the effects of surface tension gets pushed out into the tube and rectangular channel from the nozzle by a piston moved with controllable stepping motor. The velocity conditions at exit are changed as the moving velocity of pushed piston for making clear its effects. The continuous 3-D shape and reattachment of the melt-front are detected experimentally with the multi-image processing by CCD video Camera. And the flow field in the melt-front would be tried to detect as velocity vector and shear stress components from two images separated with the time.From experimental results, several interesting phenomena were detected as below. The gas-liquid interface changes its shape properties time-dependently with velocity fluctuations on vector-map near wall, which mean that there are several local and non-uniform slipping phenomena at molecular levels. Heat transfers in melt-front are also changed and correlated with the phenomena. These phenomena originated in high-polymer properties can be made useful of building the heat transfer mechanism models in order to make clear the all phenomena and to estimate the whole process of melting with a numerical simulation. Less