Heat Transfer Characteristics and Correlation of Supercritical Hydrogen Flow in Vertical Tubes: A Numerical Investigation

Supercritical hydrogen has attracted much attention due to its convenience for storage and transportation. However, its thermophysical properties undergo significant changes within a narrow temperature range under ultra-low temperature and high-pressure conditions, resulting in significant differences in its heat transfer characteristics compared to normal-pressure hydrogen. So, it is urgent to clarify the heat transfer characteristics of supercritical hydrogen under the effects of various factors. For this, numerical simulations were conducted to study the heat transfer characteristics of supercritical hydrogen flow in a vertical upward tube under uniform heat flux conditions. Based on the NIST database, the drastic changes in the thermophysical properties of supercritical hydrogen were accurately considered, and the effects of buoyancy force and flow acceleration were also taken into account. Thereafter, the influences of tube diameter (6–8 mm), heat flux (1500–3000 kW/m2), fluid pressure (5–90 MPa), and mass flow rate (0.062–0.14 kg/s) on the heat transfer coefficient were analyzed. The results showed that increasing the heat flux, tube diameter, and fluid pressure, or reducing the fluid mass flow rate, was beneficial to increasing the wall–fluid heat transfer coefficient. Furthermore, a heat transfer correlation applicable to supercritical hydrogen flow in vertical tubes within the high-pressure range was obtained, with absolute errors below 10% when applied to previous studies. These results clarify the heat transfer characteristics of supercritical hydrogen flow in vertical tubes, providing a theoretical basis for the design of a supercritical hydrogen heat exchanger in practical scenarios.