The Inside-Out Ceramic Turbine (ICT) is a promising rotor architecture that could increase recuperated microturbine thermal efficiency upwards of 40 %, by finally enabling monolithic ceramics to be used in sub-MW turbine rotors. The ICT configuration uses a structural rotating shroud which maintains rotor integrity by converting centrifugal loading to compressive stress in the ceramic blades. The shroud’s structural component is a carbon-polymer composite tape-wound hoop. Its matrix is high-temperature polyimide, which can’t operate at the rotor inlet temperature (RIT) required to achieve high efficiency. To maintain the rim’s structural integrity, an air-cooled metallic ring is used. Previous iterations of the ICT used cooling channels, which are readily machined and offer adequate cooling capacity. With the advent of metallic additive manufacturing, more specifically Laser Powder Bed Fusion (L-PBF), and the “free complexity” it brings to the designer’s toolbox, more advanced geometries can be incorporated in this critical component to increase RIT and decrease coolant mass flow.Thermal and structural loading within the cooling ring is highly orthotropic and non-axisymmetric. The blade tip, which is in direct contact with the cooling ring, induces high radial stresses and high conductive heat transfer. Due to the nature of the thermal and structural loads, pin fin cooling was deemed a promising technology for three reasons: (i) the pins can withstand the radial loading of the blades, (ii) the enhanced convective heat transfer coefficient sinks the heat conduction before it reaches the composite rim and (iii) the pin fin layout can be tuned to correspond with the load. Additively manufactured pin fins have proven to produce pressure loss and heat transfer that are difficult to model, due to very high surface roughness in small feature sizes. Therefore, experimental data is essential to design the cooling ring correctly.This paper presents the experimental characterization of additively manufactured pin fin test samples. Because of the build orientation of the pin fins and the total flow path height required according to early estimates, the test samples were designed with two stacked microchannels of 1 mm height, with a 0.5&nbsp;mm intermediate wall to ensure a proper build. The heat source was placed against the lower microchannel wall, to simulate the thermal load found in the ICT. Pressure loss and heat transfer were measured on four sample types were tested: No pins– for baseline comparison – aligned pins and two variations of staggered pins. The tested range of coolant mass flow varied from 0.01 to 0.04 g/s per mm² inlet area, at a Reynolds number range of 250 to 3700. Experimental data indicates that the upper channel contribution to heat transfer differs significantly from the lower channel, with staggered pins offering a better thermal performance, as can be expected. Tailored pin fin layouts can now be integrated in a calibrated 2D thermal model to design an efficient, stacked-channel cooling ring for the ICT.

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

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

Turbo Expo 2021

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.