EXPERIMENTAL STUDY ON GAS TRANSPIRATION COOLING WITH C/SiC CERAMIC UNDER HIGH-TEMPERATURE FLAME

Transpiration cooling technology is an efficient thermal protection method in aerospace applications. However, previous literature has generally focused on transpiration cooling with metal-based porous material, and investigations with ceramic composite as transpiration material under nonuniform high temperature flame are still inadequate. In this study, under nonuniform oxy-acetylene flame, the transpiration cooling performances with C/SiC ceramic using nitrogen gas as coolant were experimentally investigated. The experimental results reveal that under the nonuniform flame, the increased rate of central cooling efficiency was higher than at the edge with increasing the coolant flow rate. Under higher heat flux, the greater dynamic pressure of the mainstream caused more severe compression of the gas film, limiting the improvement in cooling efficiency and uniformity in top-surface temperature. At low coolant flow rate (0.50 g/s) and high heat flux (1.96 MW/m2), the temperature difference across the transpiration surface reached 287°C, which is 77°C higher than that under the lower heat-flux condition (1.22 MW/ m2). Low-porosity C/SiC exhibited higher cooling efficiency and more uniform temperature distribution at lower flow rates, while high-porosity samples performed better at higher flow rates. The high-porosity transpiration material (ε = 51.5%) exhibited 12% higher nonuniformity in cooling effectiveness than low-porosity counterpart (ε = 43.9%). Although C/SiC porous ceramics surpassed stainless steel in high-temperature endurance, their low thermal conductivity perpendicular to the fiber direction, low permeability, and irregular pore structure, C/SiC porous plates exhibited lower cooling efficiency compared with stainless steel.