Cooling Performance of Additively Manufactured Pin Fins in Stacked Microchannels for the Inside-Out Ceramic Turbine Shroud-Cooling Ring

The inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, has an air-cooled ring, which keeps its composite rotating structural shroud within operating temperature. The cooling ring must achieve a significant radial temperature gradient with a minimal amount of cooling. The cooling ring is made through additive manufacturing, which opens the design space to tailored cooling geometries. Additively manufactured pin fin heat transfer enhancers are explored in this study to assess whether they hold any significant performance benefit over current rectangular cross section open channels. Experimental friction factors and Nusselt numbers were determined for small, densely-packed pin fins over an asymmetrical thermal load. Results indicate that pressure loss is similar to what can be expected for additively manufactured pin fins, whereas heat transfer is lower due to the extremely tight streamwise pin spacing, in both in-line and staggered pin configurations. A design study presented in this article suggests that pin fins are beneficial to an ICT for reducing cooling mass flowrate up to 40%, against an increase in cooling ring mass of roughly 50%.