Experimental Investigation of Hydraulic and Thermal Properties in Additively Manufactured Channels with Air Flow

Additive manufacturing (AM) of metal alloys enables the creation of components with complex internal geometries that are often unachievable with traditional methods, offering reduced time and costs. A key application is the production of micro-channels for cooling high-temperature gas turbine components. However, the AM process introduces higher surface roughness compared to conventional methods, which significantly affects hydraulic and thermal performance, as well as material fatigue behavior. This experimental study aims to characterize the effect of relative roughness on these phenomena, focusing on two key performance parameters: the Darcy friction factor and the Nusselt number. Tests were conducted on aluminum and Inconel-939 specimens, featuring straight channels of various lengths and cross-sectional shapes, using air as the working fluid. The results revealed that, in the turbulent regime, surface roughness has a significant impact on pressure losses, increasing the Darcy friction factor compared to smooth channels. Additionally, the Nusselt number also increased due to the roughness-induced turbulence, enhancing flow mixing and heat transfer efficiency. Further analysis demonstrated that the Prandtl number does not significantly affect the Darcy friction factor, as predicted by theory, but plays a critical role in determining the Nusselt number, in line with parallel studies conducted on waterbased rigs. Although clear trends were observed, further research is required to develop predictive correlations that account for different materials and geometries.