From a micro-polymeric pipe to a mini-polymeric pulsating heat pipe

In this work, a preliminary study related to the design and manufacturing of a micro polymeric pipe for micro heat exchangers was performed. Among possible polymeric materials, a thermoplastic copolyester elastomer composed of polybuthylene-terephthalate, as crystalline phase, and long glycol chains, as the amorphous one (Hytrel® 6356, Dupont) was selected, both unloaded and loaded with 7 % w/w carbon powder. A microextrusion process was set up to obtain microtubes and the thermo-mechanical characteristics of the produced pipes were studied. Thermal properties of extruded Hytrel® remained almost the same, in terms of melting temperature (Tm ≅ 208 °C) and enthalpy change of fusion (ΔH ≅ 45 mJ/mg), although the material was C-loaded. The thermomechanical tests performed on unloaded and C-loaded Hytrel® microtubes at 25 and 70 °C (possible working temperature) detected a considerable increase in the mechanical properties of C-loaded Hytrel®, compared to the unloaded one. In particular, a relevant improvement of the elastic modulus at 70 °C for the C-loaded microtubes was observed, demonstrating a better thermal stability at high temperature. Moreover, the fabrication of a micro heat exchanger prototype and prteliminary tests with different cooling fluids confirmed the possibility of using Hytrel® for electronic applications, as a good thermal exchange was evidenced.