An investigation of porous structure characteristics of heat pipes made by additive manufacturing

Specific properties of porous media such as thermal conductivity and wicking of liquid into the porous structure are of great importance to many applications. Typically, such porous structures are found in two-phase devices, such as heat pipes (HPs). In this study, we have experimentally analysed the effective thermal conductivity and the wicking of different liquids into a stainless steel 316L porous structure fabricated through selective laser melting (SLM) technology. The sample was rectangular shaped with a porosity of 46.5% and outer dimensions of 20×40×1 mm³. An experimental apparatus and related procedures for the determination of the effective thermal conductivity of the porous structure saturated with distilled water and Ethylene glycol are discussed. The experimentally measured values of effective thermal conductivity are compared with correlations available in the literature. The standard Washburn wicking model is taken into account for the analysis. We describe the application of the Washburn equation to measure the contact angle of a printed porous sample with three test liquids; n-Hexane, water and Ethylene glycol are used to measure contact angles. The experimental results verify that SLM technology can be used to fabricate porous structures for HP technology. The results show an effective thermal conductivity in the range of 1.8-6.0 W/mK for different working fluids.