Targeted alignment of fillers in plastic pipes for increased heat transfer in heat exchanger systems.

Pipes in heat exchanger systems are usually made of metallic materials to achieve a high level of thermal conductivity and thus high efficiency. However, substitution with polymer materials has a great potential. Plastics save weight, can be produced at lower cost and emissions, and are ideal for use in corrosive or chemically aggressive environments, where most metals fail. The challenge, however, is their much lower thermal conductivity in comparison. To reduce this disadvantage, fillers are used to transport thermal energy through the less conductive polymer matrix. In fact, high filler ratios are required to achieve an acceptable level of thermal conductivity for heat exchanger systems. However, these high filler ratios have a significant impact on the material properties of the polymer, such as the flexibility, which is drastically reduced. The result is a brittle material with limited suitability for use in heat exchanger systems. This paper describes a novel approach to effectively increase the thermal conductivity of polymer materials by optimizing the orientation of anisotropic filler particles by die design. Standard pipe extrusion dies result in continuous shear forces in the direction of extrusion. Accordingly, the resulting filler network has a higher thermal conductivity in the axial direction of the pipe than radially through the pipe wall. However, radial heat transfer is essential in pipe heat exchanger systems. To improve this, various die designs for targeted radial alignment of filler particles are discussed in this paper. Furthermore, the potential for improvement of the die designs is investigated. So far, the most efficient die design achieves an increase in thermal conductivity of up to 74 % compared to a standard pipe extrusion die. [ABSTRACT FROM AUTHOR]