InterPore2026

Radiative heat transfer in porous ablators

21 May 2026, 10:05

1h 30m

Poster Presentation (MS18) High-temperature heat and mass transfer within porous materials for energy and space (T > 800 °C) Poster

Speaker

Savio Poovathingal (University of Kentucky)

Description

Porous ablative thermal protection systems (TPS) are central to the survivability of spacecraft during hypersonic and planetary atmospheric entry, where extreme convective and radiative heat loads act simultaneously on highly heterogeneous materials. In fibrous and charring ablators, such as carbon- and silica-based composites, thermal radiation penetrates beneath the surface and interacts volumetrically with the evolving porous microstructure. As a result, radiation is not merely a boundary heat flux but a dominant in-depth heat transfer mechanism that strongly influences pyrolysis, char growth, internal temperature fields, and surface recession. This work presents a multiscale modeling framework for radiative heat transfer in porous ablators that bridges material microstructure, radiative transport physics, and macroscopic material response. At the microscale, porous TPS are treated as semi-transparent, anisotropically scattering media characterized by extinction, scattering albedo, and phase function parameters that depend on fiber morphology, orientation, and wavelength. A pathlength-based reverse Monte Carlo ray-tracing (RMCRT) solver is developed to solve the radiative transfer equation (RTE) with high fidelity, enabling the explicit treatment of anisotropic scattering, spectral dependence, and spatial heterogeneity. The solver is rigorously verified against analytical solutions and benchmark problems and is shown to outperform traditional low-order approximations, such as Rosseland diffusion and P1 methods, in regimes relevant to fibrous ablators.
At the mesoscale, the RMCRT solver is tightly coupled to a material response model that solves the transient energy equation within the ablative medium. This coupling enables radiation to be treated as a volumetric source term that evolves with temperature, degree of char, and changing radiative properties. Comparative studies demonstrate that conventional diffusion-based radiative models can significantly underpredict internal temperatures, pyrolysis depths, and heating rates when anisotropic scattering or spectral effects are important. To address this, a physics-based anisotropic radiative transfer (ART) framework is introduced. The ART model combines an exponential weighted effective temperature formulation for emission with an exponential decay absorption model for incident radiation, achieving near-RMCRT accuracy at a fraction of the computational cost. At the macroscale, the framework is applied to representative spacecraft entry scenarios, including radiative heating conditions relevant to planetary missions. New metrics, such as the radiative coupling length, are introduced to quantify radiation penetration depth and identify regimes where diffusion-based models break down. Additional case studies examine radiation trapping at surface defects, estimation of effective radiative properties from X-ray computed tomography (XRCT) scans, and inverse determination of material radiative properties from experimental transmittance and reflectance data.
Overall, this work establishes a scalable, multiscale modeling approach for radiative heat transfer in porous ablators that directly links microstructural characteristics to macroscopic TPS performance. The framework provides improved physical fidelity for predicting material response under coupled convective–radiative environments and offers practical pathways for incorporating high-fidelity radiation modeling into next-generation spacecraft heat shield design and analysis.