Characterization of Heat Exchange for Additively Manufactured Components

The current work aims to develop a fundamental understanding of thermal transport mechanisms within and on AM components and structures, which is addressed through three specific objectives. The first objective is to characterize the effect of the process parameters, of FFF and SLM, on the effective thermal conductivity of AM components. Secondly, to improve the pool boiling heat transfer coefficient (HTC) using AM-based structures. Finally, to investigate the application of SLM 3D-printed evaporators in a two-phase loop thermosyphon. To achieve the first objective, a high-accuracy steady-state guarded method was developed to measure the effective conductivity of AM components. First, this apparatus was employed to measure the thermal conductivity of several PLA polymer composites, either metal or carbon fiber. The experimental results showed that all samples featured high anisotropy in thermal conductivity, reaching up to 2 in the carbon fiber composite. Thereafter, the apparatus was modified to quantify the effect of the SLM process parameters, such as the laser power, hatch spacing, etc., on the effective thermal conductivity of AlSi10Mg, which were found to significantly decrease the resulting thermal conductivity up to 22%. With respect to the second objective, an FFF-based polymer fixture was proposed to enhance the pool boiling characteristics from copper surfaces. Due to the low conductivity of the fixture, it could create a spatial temperature distribution at the boiling surface, initiating the bubbles earlier and enhancing the HTC. A high-precision pool boiling apparatus was then built, addressing most of the experimentation issues found in the literature, such as repeatability, surface aging, and the heater's small size. This device was subsequently used to examine novel 3D re-entrant cavities fabricated using SLM on the pool boiling performance. It was observed that the surface with re-entrant cavities increased the nucleation site density and the bubble departure frequency, enhancing the HTC 2.8 times compared to the plain 3D-printed surface. The last objective was achieved by investigating the difference in the thermal performance of closed-loop thermosyphon between two surfaces: machined and additively manufactured via SLM. It was shown that the 3D-evaporator slightly increased the loop thermal resistance; however, it mitigated the temperature instabilities.