Characterization of thermal conductivity in polymer composite heat exchanger parts

Fiber-reinforced, injection-molded polymer composite materials can provide heat exchanger heat transfer rates comparable to those of metallic materials. However, the relationship between fiber orientation and thermal conductivity, and its effects on the heat transfer rate need to be investigated. In this study, a methodology to determine the anisotropic thermal conductivity of an injection-molded commercially-available, thermally-enhanced polymer composite, based on numerical simulation combined with experimentation is presented. The injection molding process is numerically modeled to predict fiber orientation. The filler characteristics of injection-molded polymer composite parts are experimentally determined to derive the composite material thermal conductivity distribution using Nielsen semi-empirical model. This methodology is applied to a heat exchanger unit air channel geometry, that is virtually manufactured using either injection molding or a combination of injection molding and machining. The numerically predicted thermal conductivity values range from approximately 14 W/m.K to 16 W/m.K, depending on geometric location and manufacturing process. These values are underpredicted by up to 18% compared with laser flash measurements on physical prototypes manufactured using a combination of injection molding and machining, and are lower than the vendor-reported effective thermal conductivity (i.e., 19-21 W/m.K).