Comparison of H₂, CH₄ and H₂O for cooling an aerospace plane

This paper studies the cooling of an aerospace plane using liquid hydrogen, liquid methane, and liquid water. An ascending optimized trajectory to minimize the heat load in the hypersonic part of the flight is used to perform the study. The study includes cooling for the stagnation point, the leading edges of the wings, the engine and other parts of the aerospace plane that are close to the leading edges. The laminar case for the stagnation point and both laminar and turbulent cases for the leading edge heating have been considered. The heat rate (total, radiative and convective) and the mass of liquid coolant needed for cooling are calculated. A design for minimum inlet-outlet areas for the amount of liquid needed for cooling, is made with consideration of the coolant's physical constraints in the liquid and gaseous states. The comparison shows that liquid hydrogen is the clear winner over liquid methane or liquid water as a candidate for the coolant.