Testing a Transpiration Cooled Zirconium-Di-Boride sample in the Plasma Tunnel at IRS

Abstract

Transpiration cooling is an active thermal protection system (TPS), in which a coolant gas is fed through a porous material. This requires a material that stays structurally stable at high temperatures, while having the desired permeability. This paper explores transpiration cooling of Ultra-High-Temperature-Ceramics (UHTCs). A stagnation probe with transpiration cooled ZrB2 was tested in a plasma wind tunnel at a null point heat ux of 3.59 MW/m2 in steady state and transiently at 2 MW/m2. The aim is to understand whether transpiration cooling can increase the UHTC operating temperature by shielding it from oxygen and reducing the heating from surface re-combination. Several diagnostics are applied, including an Echelle spectrograph that explores outgassing of oxidation products from the surface. Infrared thermography is employed to track the surface temperature at the front and the back surface temperature is measured by a pyrometer. Furthermore, the Planck radiation background of the emission spectra is used to assess the front surface temperature. The testing included a variation in the injectant species and mass ux. While the uncooled sample fully oxidised at a surface temperature of 2150 K, 20.25 g/m2s of helium and 620.11 g/m2s of nitrogen prevented oxidation of the transpiration cooled samples. At a blowing parameter of 0.1094, the helium cooled probe reached a front surface temperature of 1428 K and reduced the incident heat ux by 77 % compared to the uncooled sample. The nitrogen cooled sample had a maximum front surface temperature of 1128 K with a blowing parameter of 1.958 and an 83.3 % lower incident heat ux than the uncooled sample.