Effects of oxidation on coupled heat transfer of ultra-high temperature ceramic materials at high temperature

Extreme high-temperature flight environment exposure of ultra-high temperature ceramic materials will result in their oxidations, and the generated oxide products on the surface which have different thermal-physical properties, thus will affect the heat transfer process. For pre-oxidized ZrB₂ and ZrB₂-SiC materials, the thickness of oxidation layer (ZrO₂, B₂O₃, SiO₂ and SiC-depleted layer) was calculated from oxidation models. Cylindrical representative volume unit was modeled using finite element, and it was coupled with an external hypersonic flow CFD (Computational Fluid Dynamics) solver to study the effects of high-temperature oxidation on coupled heat transfer of ultra-high temperature ceramic materials. Multi-field coupling calculation was implemented in conjunction with flow solver of Navier-Stokes equation and the finite element solver by using partition algorithm, and real time data exchange between non-matched meshes was achieved by interpolating data at coupling surface. All thermal-physical properties of ZrB₂, ZrB₂-SiC and oxidation products are temperature dependent. The effective thermal conductivity and effective heat capacity of porous medium, which are caused by the evaporation of B₂O₃ and the depletion of SiC, were calculated based on theoretical calculation. The transient coupled heat transfer analysis results indicate that, the thermal resistance of ZrB₂ after preoxidation is slightly higher than that of original ZrB₂, and there is little variation for thermal resistance of ZrB₂-SiC materials before and after oxidation. Moreover, for the same flow environmental conditions, ZrB₂ after oxidation has higher thermal resistance than ZrB₂-SiC after oxidation.