Flow and Heat Transfer Characteristics of Additively Manufactured Mini Channels

Abstract The development of Additive Manufacturing (AM) methods has enabled highly complex designs feasible to manufacture. This advancement has in turn rendered possible the fabrication of intricate cross sectional geometries that may be used as cooling passages for the future propulsion engines. These internal cooling channels may have rougher surfaces and smaller hydraulic diameters, approaching mini-channel dimensions around 1 mm, compared to conventional designs. The internal AM channel characteristics complicate the determination of the friction factor and heat convection coefficient, as they deviate from existing correlations. In this work, an AM mini-channel with relative surface roughness ε/DH = 0.025 and a rectangular hydraulic diameter of DH = 1.78 mm is experimentally tested under variable mass flow (10–35 · 10−3 kg /s) and heat flux (100–250 kW/m2) conditions. For the data demonstration the j factor of the Chilton-Colburn modified analogy is used, to combine data of different studies. The friction factor demonstrated transition to fully turbulent flow at Re ≈ 104 whereas for higher values of Re, the data showed satisfying agreement with values predicted by the Colebrook equation. The convective heat transfer coefficient correlated to the Gnielinski correlation for the range of Re number applied, but the data trendline showed a steeper slope in the j-Re diagram. This behavior could be an indication of the problem being dependent to additional parameters other than the well-established Re, Pr and f numbers.