Heat transfer and pressure loss performances for additively manufactured pin fin arrays in annular channels

Additive manufacturing technology with metal powder has facilitated the production of innovative and even more complex heat sinks. The layer-additive process offers a wide range of geometries that may be exploited for advanced cooling purposes and the final identification of the best heat sink configuration has to deal with other constraints imposed by the specific application. This contribution focuses on the thermal and fluid dynamic characterization of water cooling annular channels for applications in internal combustion engine components, where also the load-bearing capacity is requested together with the cooling performances. The heat transfer inside the annular channel was enhanced by pin fins arrays that were manufactured by selective laser melting technology in AISI 316L stainless steel. Four pin fins arrays that differ in dimensions and geometries were experimentally tested over a range of mass flow rates to compare their pressure losses and heat transfer performances against those of the smooth annular channel. Furthermore, the test coupons were analysed through optical non-destructive techniques to characterize their geometrical morphology in terms of conformity with the designed model, surface roughness and waviness. In the investigated channel Reynolds number range (from 2000 to 12,000), the pin fins arrays with the largest height-to-pin diameter ratio show better thermal performances (Nu/Nu0 always greater than 2), however their heat sink efficiencies are above unity only for Re < 3000. In addition, the 45° oriented pin arrangement seems the most promising geometry due to high thermal efficiency, lighter weight and slightly lower manufacturing cost.