Study on transpiration cooling performance of SiC porous ceramics

Ceramic matrix composites are desirable for applications in the thermal protection system of hypersonic flight vehicles due to their excellent oxidation resistance. However, the service temperature exceeds the melting point of the components with a small curvature radius. Among the active cooling techniques, transpiration cooling has been proven to be a promising thermal protection method for hypersonic vehicles. In this study, SiC porous ceramics with different geometrical shapes and open porosities are fabricated using the polymer infiltration and pyrolysis route and sacrificial template method. Theoretical analysis and experimental investigation are per -formed to explore the feasibility of transpiration cooling with various coolants for SiC porous ceramics. The results confirm that the specific heat capacity is a key parameter that affects the cooling efficiency when a gas is used as the coolant. The effects of the material's porosity, the attack angle, and the heat flux on the transpiration cooling performance with nitrogen are experimentally tested, and the highest cooling efficiency exceeded 80%. Meanwhile, the SiC porous ceramics displayed superior adaptive and self-pumping transpiration cooling per-formance when in a quartz lamp heating environment for about 10 min. The cooling mechanisms with a water phase change are also analyzed in detail. This study offers the possibility of developing thermal protection materials that could be used in active thermal protection techniques.