Numerical and theoretical evaluation of effective thermal conductivity in open-cell ceramic foams

Аuthors

Fedyunina E. R., Prosuntsov P. V.^*

Baumann Moscow State Technical University, 105005, Moscow, 2nd Baumanskaya St., b. 5, c. 1

*e-mail: pavel.prosuntsov@mail.ru

Abstract

The aim of the study is to select the rational structural parameters for a highly porous thermal insulation material, such as the parent material, characteristic pore size and surface reflectivity. To evaluate both molecular and effective thermal conductivity, geometric models of representative volume elements were developed, followed by simulations of coupled radiative-conductive heat transfer processes. Subsequently, the influence of structural parameters on heat transfer was analyzed. The effective thermal conductivity of highly porous ceramics was modeled using coupled numerical and theore-tical approaches, characterizing its temperature dependence as a function of microstructural parameters (e.g., pore morphology, fiber diameter) and material composition. The numerical and theoretical solutions demonstrate good agreement with experimental measurements for the TZMK-10 quartz ceramic material. Numerical simulations revealed a significant radiative contribution to thermal conductivity emerging at 700 K, becoming progressively dominant at higher temperatures. For fibers ≤ 2 μm in diameter, the proportion of radiative energy transfer is minimal, while for fibers ≥ 8 μm, it reaches a peak of 48,5 %. The results demonstrate that decreasing the fiber diameter, applying a low emissivity opaque coating to the fiber surface, and introducing additives into semi-transparent fibers reduce the effective thermal conductivity of highly porous ceramics. At a coating emissivity of 0,95, this approach reduces the effective thermal conductivity by 2,6 % at low temperatures (for small fiber diameters) to 22 % at high temperatures (for large fiber diameters) due to suppressed radiation transfer in the representative volume element. Compared to a semi-transparent material, opaque coatings (ε = 0,1) reduce effective thermal conductivity by 40 % at high temperatures (≥ 700 K) for fibers ≥ 8 μm in diameter.

Keywords:

highly porous insulating materials, combined radiative-conductive heat transfer, representative volume element, effective thermal conductivity, evaluation of thermophysical properties

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