Thermal conductivity of heterogeneous materials

Many usual materials are heterogeneous; they appear to be composites or sol id solutions with concentration variations. At the macroscopic scale, the e quivalent thermal conductivity can be determined from the conductivities of the components and from their spatial distribution. The analysis of differ ent models proposed in the literature for equivalent conductivity calculati on is presented. The conditions for their application are discussed regardi ng the nature of the material The main goal is to point out the criteria fo r the choice of the best models fitting to a specific case.