On friction factor of fluid channels fabricated using selective laser melting

The fabrication quality of horizontal fluid channels without supports using SLM is low, which further affects friction loss in channels. In the paper, circular fluid channels with diameters from 2 to 14 mm were built horizontally using 316L SS. The surface roughness on the top inner channel is 50-80 mu m, while the rest part is approximately 10 mu m. The cylindricity is around 0.2 and circularity is 0.16. The fabrication quality was significantly improved using reduced energy input with a compensation model. Friction factor measurements indicate that 75/Re is still valid in laminar flow regardless of fabrication quality. The friction factor in turbulent flow is 0.0034-0.0137, which is higher than the classical theory. Improved fabrication quality slightly reduces the friction factor. A corrected Colebrook model is developed to predict the friction factors for SLM horizontal fluid channels. Building orientation and fluid path need to be considered for reducing pressure loss.