Heat transfer deterioration and wall temperature non-uniformity of supercritical hydrogen in rectangular helical channels for regenerative cooling applications

Regenerative cooling using supercritical hydrogen (sH₂) is critical for managing extreme heat fluxes in liquid rocket engines. However, heat transfer deterioration (HTD) induced by drastic thermophysical property variations remains a key challenge, especially in non-straight cooling channels. This study numerically investigates the HTD characteristics of sH₂ flowing through rectangular helical coils (RHCs), with a focus on the coupled effects of thermal loading, flow parameters, and channel geometry. A validated RNG k – ε model with real-fluid properties is employed to analyze flow structure, wall temperature distribution, and heat transfer performance under representative regenerative cooling conditions. Results show that the wall temperature non-uniformity, quantitatively characterized by the WTNI, exhibits strong enthalpy dependence. Under high heat fluxes, the earlier pseudo-critical transition near the wall shifts the local peaks. Increasing system pressure suppresses HTD and stabilizes wall temperature distribution, whereas higher mass velocity under constant q _w/G aggravates wall temperature non-uniformity. Geometrically, reducing channel width significantly enhances heat transfer coefficient (up to 35.4%) and mitigates WTNI by intensifying transverse momentum exchange, while coil diameter mainly influences temperature redistribution rather than global heat transfer. These findings provide quantitative understanding of HTD evolution in rectangular channels and offer practical guidance for the design of high-performance regenerative cooling systems.