Thermal–hydraulic–mechanical characteristics of a double-layer cooling channel using supercritical CO₂ and n-decane as coolants

The demand for higher flight speeds presents a significant challenge for traditional regenerative cooling systems. To address the limitations of insufficient cooling sources, this study proposes a double-layer cooling scheme utilizing n-decane and supercritical CO₂ (SCO₂) as coolants. A thermal–hydraulic–mechanical numerical model, accounting for the thermal cracking of n-decane, is developed and comprehensively validated. Considering the arrangement of the two coolants, four cases are investigated. The results indicate that the BDF form consistently maintains a higher overall channel temperature increasing by 50–80 K, leading to more severe heat transfer deterioration. Among the double-layer schemes, the CDF scheme with n-decane in the inner channel shows the best cooling performance with the average temperature is 43–128 K lower than that of the other three cases, Compared to the traditional single-layer method, the using of SCO₂ reduces the n-decane mass flow rate by 1.04 g, while decreasing the overall channel temperature by 121 K. Flow field analysis reveals that the twisting of streamline and the maldistribution of mass flux occur simultaneously with heat transfer deterioration. Furthermore, the heat transfer deterioration of n-decane results from the both effects of buoyancy and flow acceleration, while SCO₂ is primarily influenced by flow acceleration. Additionally, stress investigation indicates that the form using n-decane in the inner channel results in a lower stress level, with the equivalent stress reduced by 10%–20%. The maximum stress within the cross-section occurs in the thin walls between channels where shows a nonlinear stress distribution. And gradually transitions to a linear pattern as the pressure increases. Strength evaluations for all test cases meet the ASME requirements.