Thermal diffusivity of dispersed composites

The thermal diffusivity of a series of copper whiskers‐copper spheres dispersed in solder was measured by the flash method at room temperature. These diffusivity values are compared with the calculated thermal diffusivity values using effective thermal conductivity values computed with Maxwell’s dispersion equation. The results show that the concept of an effective thermal diffusivity is valid at least for particle‐to‐matrix diffusivity ratios between 1 and 3.5 and volume specific heat ratios between 0.02 to 0.52 in randomly dispersed composites containing up to 30 volume% of dispersed particles. These results were not influenced by changing the particle size or shape over fairly wide ranges (at room temperature). The conditions of heterogeneity used were far outside the limits implied by a previous mathematical derivation.