Assessment of Additive Manufactured Micro-Channel Characteristics: Impact of Hydraulic Diameter Evaluation

Abstract

Among internal cooling techniques for gas turbine components, skin cooling is recognized as one of the most promising, especially thanks to the spread of additive manufacturing (AM) techniques. In this regard, several studies have tried to characterize heat transfer and pressure loss performance of additive manufactured micro-channels, as well as the impact of AM characteristic parameters, mainly in the form of building angle, and resulting surface roughness and channel shape. The open literature offers several correlations in terms of friction and heat transfer coefficient using a representative hydraulic diameter. Despite that, little attention is given on the importance of such characteristic length definition which may lead to under/over estimation of the cooling rates when correlations are used in the design. In this work, coupons featuring circular micro-channels with diameters of 0.5 and 1 mm and different building angles have been tested, to retrieve pressure losses and an average heat transfer coefficient through a lumped approach. The coupons were additive manufactured using the laser powder bed fusion technique. Exploiting the experimental survey, the impact of the considered hydraulic diameter was investigated, by comparing different approaches based on a direct measurement. An additional and new approach, aimed at the identification of an “effective” diameter, based on fluid-dynamic considerations, was also considered. The data correlation and the comparison with available correlations from different authors showed the newly proposed approach to provide superior scaling capabilities and, in turn, allowing for the development of more accurate prediction methods.