An 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).
