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Prediction of Effective Thermal Conductivity of Refractory Materials at High Temperatures based on Synthetic Geometry Generation

C. Demuth¹, J. Hubálková², M.A.A. Mendes^1,3, F. Ballani⁴, D. Trimis^1,3, S. Ray¹

¹ Institute of Thermal Engineering, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Straße 7, D-09596 Freiberg, Germany
² Institute of Ceramic, Glass and Construction Materials, Technische Universität Bergakademie Freiberg, Agricolastraße 17, D-09596 Freiberg, Germany
³ Engler-Bunte-Institute, Division of Combustion Technology, Karlsruhe Institute of Technology, Engler-Bunte-Ring 7, D-76131 Karlsruhe, Germany
⁴ Institute of Stochastics, Technische Universität , Prüferstraße 9, D-09596 Freiberg, Germany

received January 11, 2016, received in revised form March 21, 2016, accepted April 13, 2016

Vol. 7, No. 2, Pages 183-192   DOI: 10.4416/JCST2016-00006

Abstract

In the present article, the numerical prediction of the effective thermal conductivity (k_eff) of low-carbon refractory materials at high temperatures is investigated. The employed numerical methodology consists of computational geometry generation by a modified random sequential adsorption (RSA) algorithm and solution of a heat conduction problem in the generated material sample by the finite volume method (FVM). The probability distributions, employed for modelling the grain sizes, are reexamined. Several aspects are recognised as crucial for reasonable predictions of k_eff in the considered range from the room to the coking temperature. First, an appropriate estimate of the equivalent thermal conductivity k_rest of the unresolved fine-scaled material is required, which is obtained from the effective medium theory (EMT). Furthermore, modelling the thermal expansion of the coarse and medium grains, leading to the formation of air gaps between the grains and the continuous phase at lower temperature, is extremely important. The presence of these air gaps could be implemented in FVM. The numerical predictions of k_eff show reasonably good agreement with experimental data in the complete temperature range, only if this gap width is considered as a function of the operating temperature, along with k_rest and the temperature-dependent thermal conductivities of the constituents.

Keywords

Effective thermal conductivity, refractory materials, random sequential adsorption, finite volume method, thermal contact resistance

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