High temperature two-phase thermal conductivity of ceramic sponges with stagnant fluid – Experimental results and correlation including thermal radiation

Abstract

Experimental results for the two-phase thermal conductivity (often called “effective thermal conductivity”) with stagnant fluid at temperatures up to 1200 K for different ceramic sponges (variation of material, porosity and cell density) are presented in this publication. A two-plate test facility was used for the experiments. Samples investigated have porosities higher than 75% and cell densities in the range of 10–45 ppi (pores per linear inch). They are made of alumina, mullite and oxidic-bonded silicon carbide. The two-phase thermal conductivity is strongly dependent on temperature, porosity and cell sizes of the sponge sample. A model based on the superposition of the two heat transfer mechanisms, thermal conduction and thermal radiation is used to predict the two-phase thermal conductivity of ceramic sponges. A model based on combination of thermal resistances is suggested for predicting the thermal conductivity. The so-called Rosseland equation is used as an initial model for predicting the part of thermal radiation on the two-phase thermal conductivity. Measurements of material properties are included in this work as model implementation requires an exact knowledge of sponge data.