SGER: Flow-induced anisotropic thermal energy transport in elongational flows of polymer liquids

CBET-0837907Venerus提出了拉伸变形下聚合物熔体流动诱导各向异性导热的实验研究。在以前的研究中，我们开发并应用了一种新的光学技术来定量测量聚异丁烯熔体剪切流动中的导热张量。这些以前的研究结果与应力-热定律是一致的，即应力和导热张量是线性相关的。在本研究中，同样的光学技术被应用于简单拉伸流动中的聚合物熔体。热导张量的两个分量(平行和垂直于拉伸方向)将作为应变和应变率的函数进行随时间的测量。此外，在相同的流动中获得了力学(应力)和光学(双折射)数据。首次利用导热系数和应力数据检验了聚合物熔体拉伸流动中应力-热规律的有效性，以及具有不同化学组成的聚合物的应力-热规律的有效性。目前和以前的实验结果被用来从分子水平上理解聚合物中流动诱导的各向异性热传导。在纤维纺丝和注射成型等制造过程中，聚合物熔体的流动本质上是非等温的。因此，这些工艺的有效设计和操作依赖于对流动的聚合物熔体中的热传输的良好了解。尽管有这种公认的重要性，但变形聚合物液体中的热传递，特别是流动诱导的各向异性热传导，人们知之甚少。精确的计算机辅助设计聚合物过程需要一个模型来估计作为变形或应力的函数的导热系数。本研究获得的实验结果直接满足了这一需求。这项研究的结果对发展聚合物中流动诱导各向异性热传导的预测性或半预测性理论也将是非常有价值的。该项目由热传输过程(TTP)计划和流体动力学(FD)计划联合资助，这两个计划都是由工程局(ENG)的化学、生物工程、环境和运输系统(CBET)部门共同资助的。

CBET-0837907VenerusAn experimental study of flow-induced anisotropic thermal conduction in polymer melts subjected to elongational deformations is proposed. In previous studies, we have developed and applied a novel optical technique to obtain quantitative measurements of the thermal conductivity tensor in shear flows of poly-isobutylene melts. Results from these previous studies are consistent with the stress-thermal rule, which says the stress and thermal conductivity tensors are linearly related. In the present study, the same optical technique is applied to polymer melts in simple elongational flows. Time-dependent measurements of two components of thermal conductivity tensor (parallel and perpendicular to the stretch direction) will be obtained as functions of strain and strain rate. In addition, mechanical (stress) and optical (birefringence) data are obtained in the same flows. The thermal conductivity and stress data are used to examine for the first time the validity of the stress-thermal rule in elongational flows of polymer melts, and the validity of the stress-thermal rule for polymers having different chemistries. Experimental results from the present and previous studies are used to develop a molecular-level understanding of flow-induced anisotropic thermal conduction in polymers.Flows of polymeric melts in fabrication processes such as fiber spinning and injection molding are inherently non-isothermal. Consequently, the efficient design and operation of these processes relies on a good understanding of thermal transport in flowing polymer melts. Despite this well-accepted importance, heat transfer in deforming polymer liquids, and in particular, flow-induced anisotropic thermal conduction, is poorly understood. Accurate computer-aided design of polymer processes requires a model for estimating the thermal conductivity as a function of deformation or stress. The experimental results obtained in this study directly address this need. Results from this investigation will also be invaluable in the development of predictive, or semi-predictive, theories for flow-induced anisotropic thermal conduction in polymers.This project is jointly funded by the Thermal Transport Processes (TTP) Program and the Fluid Dynamics (FD) Program, both of the Chemical, Bioengineering, Environmental, and Transport Systems (CBET) Division within the Directorate for Engineering (ENG).