“Vapor blockage” and aqueous oxidation in C/SiC porous ceramic during transpiration cooling with phase change

Transpiration cooling with phase change is a promising method for thermal cooling of hypersonic flight and scramjet engine for its outstanding cooling efficiency. However, superheated vapor generated inside the porous plate will lead to local overheating. Nevertheless, the relation between uniformity of incoming stream and vapor-blockage effect in porous ceramic was seldom investigated. Moreover, the aqueous oxidation corrosion of C/SiC in transpiration cooling remains underreported. Herein, we explore the transpiration cooling under the non-uniform high-temperature flame and validate the erosion mechanism during transpiration cooling with water inside the C/SiC porous material. Results show that expanded vapor in central zone and the low thermal conductivity of vapor are responsible for the increases of top-surface temperature, radial-temperature difference and inlet-pressure fluctuation. The decrease in porosity increases the effective thermal conductivity of the porous plate, leading to a higher center temperature, and a lower edge temperature. Temperature and inlet pressure oscillations, caused by the reciprocating vapor expulsion and regeneration, exhibit a 273 s average period with center temperature and pressure amplitudes of 796 °C and 0.9 kPa, respectively. After experiment, corrosion cracks due to aqueous oxidation are observed on the specimen surface with the weight loss of 8.6 % and chemical production of H₂Si₂₀O₄₁·xH₂O.