Thermal conductivity of heterogeneous materials

Many usual materials are heterogeneous; they appear to be composites or solid solutions with concentration variations. At the macroscopic scale, the equivalent thermal conductivity can be determined from the conductivities of the components and from their spatial distribution. The analysis of different models proposed in the literature for equivalent conductivity calculation is presented. The conditions for their application are discussed regarding the nature of the material The main goal is to point out the criteria for the choice of the best models fitting to a specific case.