Optimizing longitudinal geometries of ultra-low temperature sintered heat exchangers

Dilution refrigerators achieve millikelvin temperatures crucial for quantum computing and low-temperature physics, with sintered metal powder step heat exchangers (SHEs) being critical components for precooling ³He and maintaining base temperatures. However, accurate SHE performance evaluation is challenging due to manufacturing complexities and difficult cryogenic measurements. Existing one-dimensional numerical models oversimplify intricate geometries, highlighting a critical lack of comprehensive three-dimensional investigation into longitudinal runner geometrical configurations and their impact on heat transfer. Therefore, this study employs 3D numerical simulations, comparing linear and curved SHEs and exploring the optimization potential of various curvatures and multi-stage designs. Results show that curved SHEs offer no significant overall performance improvement over linear designs, and increased curvature unfavorably raises the concentrated phase outlet temperature. While multi-staging effectively reduces outlet temperature, diminishing returns are observed. Importantly, optimized uneven multi-stage designs, such as a three-stage configuration, achieved superior performance by reaching lower concentrated phase outlet temperatures than even equally divided four- and five-stage designs, highlighting the effectiveness of allocating more heat transfer area to stages exhibiting the smallest temperature drop proportion. This research provides novel insights and critical guidance for designing high-efficiency heat exchangers in future dilution refrigerators, advancing quantum technology and cryogenic science.