THE EFFECTIVE THERMAL-CONDUCTIVITY OF A MULTIPHASE SYSTEM

The transient plane source technique (TPS) is used at low temperature to measure the thermal conductivity of two polycrystalline granite sam ples. A brief description of the technique is included. Our measuremen ts revealed that both samples exhibited weakly temperature dependent c onductivity in the relevant temperature range. An attempt was made to examine the problem of determining the bounds and/or estimating the ef fective thermal conductivity of a multiphase system given the volume f ractions and the conductivities of the components. The attempt was to compare the measured data at room temperature with theoretical results . These results are obtained using different models including those of the Effective Medium Theory (EMT), Hashin and Shtrikman (HS) bounds, Wiener bounds, and weighted geometric mean model. The models can be us ed to characterise macroscopic homogeneous and isotropic multiphase ma terials either by determining the bounds for the effective thermal con ductivity and/or estimating the overall conductivity of the random mix ture. According to our calculations for these kinds of crystalline roc ks, the effective medium theory produced calculated results that agree d best with the measured conductivity values.