Thermal Analysis of Calcium–Magnesium–Alumino–Silicate Infiltration Dynamics in Thermal Barrier Coatings

Modeling molten droplet spreading and infiltration into non-isothermal thermal barrier coatings

“…where keff is the effective thermal conductivity. The value of qs ″ is chosen to create the designated initial top surface temperature commonly used in existing studies [14,15,41]. We also approximate that qs ″ is not affected by the presence of the droplet on the topcoat throughout the infiltration process due to the droplet's small size.…”

“…Heat transfer by convection of the molten CMAS is neglected due to the low Péclet number as analyzed in Munuhe et al [41]. In addition, perfect contact between the spreading droplet and the porous medium is assumed such that:…”

“…At the infiltration front in the porous medium, which separates two domains with different thermal properties, continuous temperature and heat flux is enforced. Within the wetted region, the effective thermal conductivity is assumed isotropic, and this assumption is justified by the minimal difference in thermal conductivity between CMAS and 7YSZ [41]. In the dry region, the effective thermal conductivity is supposedly anisotropic due to the columnar microstructure.…”

“…Considering the low porosity and strong radiation heat transfer across the gaps between columns, heat conduction in the dry region is assumed as isotropic as well. Effective thermal conductivity and specific heat capacity in the wetted region are calculated using the following equations [41]:…”

“…To enhance resistance to CMAS infiltration, the TBC top layer can be fabricated to possess heterogeneous structures with varying pore microstructures. Such a morphology reduces the infiltration rate by limiting wetting interactions and/or using low-permeability microstructures [41]. To achieve an optimized microstructure, there is a need for better understanding of how heterogeneous microstructures affect CMAS droplet infiltration behavior in porous TBC topcoats.…”