Experimental investigations of transpiration cooling applied to C/C material

In today's rocket thrust chambers extremely high heat loads are apparent. Reducing these loads in combination with a reduction of the thrust chamber's structural weight can be achieved with transpiration cooling applied to composite carbon/carbon materials (C/C). This article presents the results from transpiration cooling tests in subsonic main-flow at Mach numbers between M_g = 0.3 and M_g = 0.7 while total temperatures of up to T_t,g=523 K were reached. As coolant air was used as a reference, combined with tests using argon and helium. Four different C/C samples were investigated, varying the thickness and porosity of the material. During the tests, detailed information of the surface temperature of the transpiration cooled C/C samples was obtained using infrared thermography. Then, the cooling efficiency of the porous wall at different main-flow conditions was assessed. It was pointed out, that the main-flow total temperature, wall thickness and material charge or porosity do not influence the cooling behavior in the range tested, whereas the main-flow heat load and coolant used show a significant impact. Temperature profiles within the sample were recorded in addition using thermocouple measurements to investigate the thermal behavior and the assumption of thermal equilibrium within the wall in more detail. Based upon these observations, it is shown that models from literature can be used for the prediction of transpiration cooling effects with foreign gas injection for the investigated materials if the non-adiabatic test environments are taken into account.