Heat transfer and topological characterisation of TPMS structures using 3D printed materials

• TPMS heat exchangers of varying materials recover the same Reynolds-Nusselt curves. • Computed tomography (CT) may be used to quantitatively assess 3D print quality. • Source STL files may be insufficient for 3D print characterisation. • TPMS resin prints show promise for rapid systematic research investigations. In this paper, we conduct a quantitative assessment of the print quality and heat transfer performance of micro-structured heat exchangers created using additive manufacturing using different 3D printed materials. Starting with a single base file for printing, five cubes filled with channels derived from a triply periodic minimal surface (TPMS) were 3D printed. Micro-computed tomography (μCT) was used to measure the topological parameters defining the TPMS structures, specifically the porosity and hydraulic diameter. The porosity and hydraulic diameter of the sintered alumina structure showed differences of approximately 7 % and 10 % respectively compared with the file they were originally constructed from; the aluminium and nylon materials showed similar deviations, while the resin and green alumina demonstrated deviations approximately halved in magnitude. Experimental measurements of the film heat transfer coefficients were performed over the range 400< Re <2500 on the sintered alumina, aluminium, and resin structures, covering a wide range of thermal conductivities. All materials were found to produce results on the same Reynolds versus Nusselt number curves when the topological parameters were measured accurately using μCT. However, if the Nusselt numbers were calculated using the as-designed topological parameters, and not the μCT parameters, differences of up to 20 % were observed, significantly altering the agreement between the tested materials. These results give confidence in the air-side film heat transfer coefficients measured. They also demonstrate the viability of using simple and low-cost resin printed parts to develop heat transfer correlations within the region tested, provided the structure of the 3D printed part is known precisely.