Experimental and numerical investigation of heat transfer deterioration in upward vertical flow of supercritical hydrocarbon fuel

Regenerative cooling technology holds significant promise for high-Mach-number propulsion systems. In such systems, hydrocarbon fuels enter supercritical states, exhibiting highly nonlinear thermophysical property variations and anomalous heat transfer behavior. This study conducts a systematic experimental investigation of the heat transfer characteristics of supercritical hydrocarbon fuel under varying heat flux and mass flow rate conditions. The wall-temperature-based criterion is employed to classify heat transfer regimes along the flow path, revealing that heat transfer deterioration (HTD) occurs under conditions of high heat flux and low mass flow. Building on these observations, a coupled numerical model is utilized to explore the underlying mechanisms of HTD and its influence on thermal stress. It is found that the velocity profile evolves from a “U” shape to an “M” shape due to thermal acceleration. The thermal acceleration effect leads to stratification of velocity and density. This results in the formation of a laminarized boundary layer and a consequent reduction in turbulent kinetic energy. The flow and thermal stratification severely hinder the efficient transport of heat from the near-wall region to the core flow. The temperature rise causes the near-wall thermal conductivity to decrease by nearly 50%, thereby increasing the thermal-conduction resistance. The resulting increase in local temperature gradients leads to a 6.6% rise in thermal stress. These findings offer valuable insights for the design of cooling channels and the safe operation of regenerative cooling systems.