Numerical investigation of rocket engine cooling channel heat transfer for different LNG under trans-critical conditions

Hydrocarbon impurities in Liquified Natural Gas LNG may produce undesired phenomena such as pseudo boiling and two-phase flow. This can be an issue for rocket engine cooling channels. This study investigates the impacts of hydrocarbon impurities on LNG thermophysical and transport properties. It estimates the required relative roughness to improve the cooling capabilities with appropriate pressure drops for different LNG mixtures flowing in the rocket engine cooling channel. The Reynolds-averaged-Navier–Stokes equations are numerically solved for a straight cooling channel with a circular cross-section and uniform heat flux. LNG’s thermophysical and transport properties are calculated using the GERG equation of state and extended corresponding states, respectively. The turbulent models are validated numerically for supercritical LNG, vapor methane, and supercritical hydrogen. The results show that hydrocarbon compositions play a significant role in cricondenbar pressure. When the hydrocarbon impurities increase, the phase envelope develops, and cricondenbar pressure increases. The impacts of various relative wall roughness configurations on the cooling capabilities and pressure drops are sensitive under transcritical processes and hydrocarbon compositions. This study provides a systematic understanding of the relationships between cooling channel surface roughness, Nusselt Number, and LNG composition, offering designers the ability to optimize heat transfer in rocket engine cooling systems.