Research on heat transfer characteristics of supercritical hydrogen in rough U‐shaped channels

Abstract To explore hydrogen's cooling performance and mechanism as a coolant in heat exchangers, the RNG k‐ε turbulence model is employed to simulate the heat transfer characteristics of supercritical hydrogen within U‐shaped tubes. The influence of factors such as the heat‐to‐mass ratio, hydraulic radius, and roughness on the flow and heat transfer characteristics is analyzed. Emphasis is placed on exploring the mechanism by which the introduction of roughness enhances heat transfer. A new heat transfer correlation equation is established. The results show that for vertical U‐shaped tubes under cooling conditions, increasing surface roughness or reducing the heat‐to‐mass ratio and hydraulic radius significantly enhances heat transfer. Compared to increasing the mass flow rate, reducing the heat flux and consequently lowering the heat‐to‐mass ratio can increase the heat transfer coefficient by approximately three times, with less heat transfer decay at the outlet section. Dimensionless number analysis reveals that buoyancy and flow acceleration effects have negligible impacts on heat transfer during hydrogen flow. However, centrifugal forces alter the circumferential thermal property gradients, effectively enhancing heat transfer in the curved sections. Finally, the proposed heat transfer correlation based on surface roughness predicts an accuracy deviation of ±20%, making it suitable for predicting the heat transfer of supercritical hydrogen.