<p>The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment. However, such extreme operating conditions pose&nbsp;a severe challenge to the heat exchanger design. Although recently developed super alloys and ceramics can survive high temperatures and high-pressure loads, using these materials in a traditional heat exchanger design requires high cost and yields low power density.&nbsp;In this work, we propose a high power density ceramic heat exchanger for high-temperature applications enabled by a multiscale porous design. In each macrochannel which is on the scale of 5 mm to 1 cm, we construct a 2D array of microchannels, which are on the scale of 0.1 mm. The array of microchannels forms a scaffold structure that not only provides efficient heat transfer through the solid phase, enhances the heat transfer areas, but also strengthens the heat exchanger to overcome the significant pressure differences between two working fluids. In this work, we analyze and design an&nbsp;air-sCO2 heat exchanger for hybrid/electric aviation APUs with this numerical model. We build&nbsp;a hierarchical thermal-fluidic numerical model with COMSOL software to predict the pressure drop, heat exchanger effectiveness, volumetric and weight power density as well as the thermal capacity. Additionally, we use an effective medium approach to simulate the mechanical strength of the scaffold structure formed by the microchannels. An optimized design is expected to achieve high power density, light weight, low cost&nbsp;along with less than 4% pressure drop penalty. By optimizing the design of centimeter-scale macrochannels and micrometer-scale microchannels, signiﬁcant improvement to both the heat transfer and structural strength are predicted, with a negligible pressure drop penalty, compared to current state-of-the-art solutions. The designed high temperature heat exchanger can be readily fabricated with a co-extrusion process, utilizing commercial ceramic powders such as SiC or other super alloy powders. The scalable fabrication process and the low requirement on the materials significantly reduce the cost of the heat exchanger.&nbsp;Furthermore, the heat exchanger design is customizable for different applications in hybrid and electric aerospace applications, as well as terrestrial power generation such as nuclear power generation and concentrated solar power generation. By adjusting the microchannel sizes, the heat exchanger can be applied in a CSP plant where molten salt and sCO2 are the working fluids. Overall, the proposed high temperature heat exchanger&nbsp;promises more than 2.5x&nbsp;thermal performance compared to state-of-the-art solutions utilizing commercially available superalloy and ceramic materials, while providing the benefits of low cost, scalable fabrication, low pressure drop and high structural strength.</p>

Multiscale Porous High-Temperature Heat Exchanger Design Using Ceramic Co-Extrusion

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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