Heat transfer characteristics of supercritical CH 4 – N 2 mixtures in a precooling cycle

Abstract To address the unclear heat transfer mechanisms and lack of systematic parametric studies for supercritical CH 4 – N 2 mixtures in hydrogen liquefaction precooling systems, a numerical investigation using the RNG k–ε turbulence model is conducted. The effects of N 2 ratio (0%–40%), heat flux (30–60 kW/m 2 ), and mass flux (120–210 kg/(m 2 · s)) on heat transfer performance are analyzed. Results show that increasing N 2 ratio weakens overall heat transfer, with top wall deterioration changing significantly, while bottom wall heat transfer always exceeds that on the top wall. Higher heat flux reduces heat transfer coefficients on both walls and worsens deterioration. Top wall deterioration is dominated by thickening of the thermal resistance layer; bottom wall behaviour reflects competition between buoyancy driven local enhancement and overall attenuation. Increasing mass flux improves coefficients on both walls and suppresses deterioration. Top wall heat transfer is jointly influenced by a low‐density fluid and pseudo‐critical effects, whereas the bottom wall maintains good performance. Based on simulation data, a concentration parameterized heat transfer correlation is established with prediction errors within ±15%. Compared with an existing concentration weighting correlation, the new correlation reduces the mean relative deviation by 9.253%, enabling more accurate prediction. This study provides theoretical basis and data support for optimizing hydrogen liquefaction processes and designing precooling heat exchangers.