HEAT-TRANSFER BY CONDUCTION AND RADIATION IN SEMITRANSPARENT MATERIALS

We show here an adaptation of the classical Flash Method permitting th e measure of the thermal conductivity of semi-transparent porous mater ials. A flash lamp sends a heat pulse on the upper face of a cylindric al sample and lower face temperature is analysed. The semi-transparent material is sandwiched between two copper slices. The sample used sca tters thermal radiation, and absorbs it very little. It is therefore p ossible to account for two parts of heat transfer through the material : a pure conductive phenomenon and a radiative one. In most insulating materials radiative transfer represents about 1/3 of the total heat f lux at the ambiant temperature. The problem is solved with electrical analogy, quadripoles technique and Laplace transform. The modelization brings out two physical character parameters of the material and a co efficient qualifying the thermal exchange between the sample and the e nvironment during the experiment.