Developing Gravity-Dependent Similarity Criteria for Flow Boiling Critical Heat Flux: A Data-Driven Method

Two-phase heat transfer loops are a promising technology for spacecraft thermal management due to their efficient heat dissipation, long-distance heat transport capability, and precise temperature control. A critical parameter in designing these systems is the critical heat flux (CHF), which is sensitive to gravitational conditions. Validating CHF under varying gravity levels, however, is experimentally challenging and costly. Similarity criteria offer practical alternatives, enabling ground-based scaled experiments to simulate microgravity phenomena, though existing criteria lack universality and quantitative rigor. This study applies a data-driven dimensional analysis method, integrating the Buckingham Pi theorem with the active subspace approach, to systematically investigate CHF under microgravity conditions. Based on a comprehensive dataset of 2298 points, two dominant dimensionless numbers were identified, with the most influential number exhibiting a clear power-law correlation with the boiling number (BoCHF) and a subtle gravitational dependency (proportional to g0.06). The derived gravity-dependent similarity criterion enables effective laboratory-scale modeling of CHF behavior under microgravity, potentially reducing reliance on costly space-based experiments. The findings offer a practical foundation for enhancing thermal management system design in future space missions.