Design, Fabrication, and Hydrodynamic Characterization of an Additively-Manufactured High Power Density Multi-Pass Microchannel Heat Exchanger for Extreme Environment Applications

This study designs and fabricates a small-scale, counter-flow Multi-Pass Microchannel Heat Exchanger (MPMHX) with a high surface area density of 989 m2/m3 using selective laser melting printing process, achieving a power density of 45.4 MW/m3. The MPMHX features fin and microchannel widths of 0.180 mm and 0.762 mm, respectively, to enhance power densities with sCO2. The ribbed manifolds ensure uniform flow, while the 173 mm multi-pass microchannel array was designed with the manifolds to fit within the printer volume. The high compactness of the HX poses printing challenges. So, the printing orientation, support structures, and printing parameters were developed to successfully fabricate the HX with a measured porosity of 3.8 % using the buoyancy method. Additionally, the long, narrow channels complicate powder removal. Therefore, a two-step process was developed, consisting of ultrasonic cleaning and pressurized air cleaning. Afterwards, the fabricated microchannels exhibited a relative roughness of 9.6 %, increasing pressure drop by 165 % compared to smooth channels. This study demonstrates that additive manufacturing can successfully fabricate MPMHX without substantial channel clogging, defects, or inaccuracies that hinder performance. It also provides clear guidance for future research on HX fabrication using additive manufacturing, paving the way for advanced highpower-density heat exchangers.