Experimental and theoretical investigation on the influence of surface emissivity on the thermal conductivity of insulating materials

The theory of heat transfer through semi-transparent insulating materials explains the importance of thermal radiation in the overall heat transfer. In many semitransparent insulating materials the influence of radiation is such that the boundaries surface emissivity have a considerable influence in measured thermal conductivity. In this work the heat transfer through low density polystyrene has been investigated theoretically and experimentally. A preliminary experimental work to determine the emittances of several reflective foils (aluminum, silver and gold) by heat flow meter apparatus measurements has been done. Then thermal conductivity measurements with heat flow meter apparatus on a low density polystyrene board has been performed at 283 K and 293 K. The measurements were repeated with the surfaces of the apparatus uncoated and with the specimens enclosed in the reflective foils . An accurate simple model for the overall thermal resistance is presented. A good agreement between the predicted model thermal resistance and experimental measurements has been found.