Tomography-based radiative characterisation of decomposing carbonaceous heat shield materials

Abstract

a b s t r a c tThis work evaluates the changes in radiative properties of two decomposing carbonaceous porous materials, each composed of two semi-transparent, homogeneous and isotropic phases. The understanding of the complex dependence of macroscopic optical behaviour on material microstructure, bulk phase properties and the wavelength of incoming radiation is paramount for modelling, design and optimisation of systems incorporating such media. Experimental and numerical techniques were combined to solve the homogenised radiative transfer equations using Monte Carlo ray tracing in the limit of geometrical optics. Effective radiative properties required by these equations were determined by Monte Carlo techniques using the exact 3D microstructures of the samples, obtained through high-resolution synchrotron computed tomography. This methodology is applied to a medium density carbon phenolic and a high density graphite reinforced polymer composite, each composed of semi-transparent solid and fluid phases. The extent of material decomposition is seen to affect the absorption behaviour of both samples. This effect is more obvious in the lower density carbon phenolic, where an 18% increase in absorptance is observed due to decomposition, compared to an increase of just 2% for the graphite. A library of absorption data is presented for use in continuum heat transfer modelling of similar chemically reacting macroporous carbon composites.

Radiative characterization of random fibrous media with long cylindrical fibers: Comparison of single- and multi-RTE approaches

“…(2) - (6) are the general form of volume-averaged RTEs in heterogeneous two-component medium. Specifically, these equations take into account that the medium hosting the fibers and the fibers themselves may absorb and scatter radiation [41] . In that case, the radiation propagation in the phase i (air or fiber substance) can be described by intrinsic radiative properties namely intrinsic extinction β int, i , absorption κ i , and scattering coefficients σ i , and phase function i .…”

A modified zonal method to solve coupled conduction-radiation physics within highly porous large scale digitized cellular porous materials

“…Cellular materials [1] such as open-cell foams, manufactured lattices, fibers felts exhibit interesting properties such as high strength-to-weight ratio, high surface-to-volume ratio, good flow-mixing capacity which make them suitable for several engineering applications. Certain high temperature applications where cellular porous materials are used include solar power power plants [2][3][4], heterogeneous combustion [5], thermal protection systems [6][7][8][9], etc. Note that, for porous samples having mean characteristic size of their constituents greater than a few microns or much greater than the size of thermal radiation can also be refereed as macroporous materials [10,11].…”

Determination of the longitudinal thermal conductivity of low‐ordered carbon fibers by using an optothermal Raman technique

“…Advanced materials made of CF such as carbon-carbon composites, CF reinforced composites, and reinforced carbon-carbon are widely used as filtration membranes, 1 electrodes of fuel cells, 2,3 braking systems in aerospace and automotive industries, 4,5 and thermal protection systems. [6][7][8][9][10] With continuous advancement in material technology, the study of thermal properties of these materials has been an interesting topic for researchers and industrialists.…”

“…Many efforts have been devoted to correctly estimate the thermal properties (e.g., specific heat capacity, thermal diffusivity, and thermal conductivity) of above mentioned materials at different scales either through experimental 10,11 or numerical means. 6,7,10,12,13 Although the methods to estimate thermal properties at macroscopic scale have been discussed in numerous studies, very limited information for microscopic materials such as CF can be found. This is not only due to the microscopic size of the fibers which requires advanced tools but also due to the large variation of the thermal conductivity of these materials with temperature and their structural organization.…”