Experiment and theory of thermal transport properties of heterogeneous composites

The three-dimensional N112 carbon-fibre-reinforced carbon material has been characterised with respect to its microstructure, which is orthorhombic. The temperature dependence of specific heat capacity, density, and-independently-thermal conductivity and thermal diffusivity of this material has been measured. The representative volume element has been modeled for simulations by the finite element method of steady-state and nonsteady-state heat transfer, with the ratio of thermal conductivity of the fibres to that of the matrix (filling material) varied from 1 to 100. The results confirm the experimental findings that the sample size in the direction of heat flow is of major importance for the determination of true thermal transport properties. A distinct difference has been found for the critical length between the steady-state and nonsteady-state cases.