THERMAL-CONDUCTIVITY OF CELLULAR CARBON FOAMS - FLASH METHOD MEASUREMENTS AND ANALYSIS

This paper deals with the thermal diffusivity measurement of cellular carbon foams by the posh method. The thermal conductivity is obtained from the thermal diffusivity by using specific heat and density of car bon foam. These materials constitute non-homogeneous porous semitransp arent media, hence the classic experimental set-up of the posh method must be adapted. A study is carried out in order to show the influence of the sample thickness, of the temperature, of the enclosed gas pres sure and of the gas composition on the effective thermal conductivity. Identification functions are established in the monodimensional and b idimensional cases. Results indicate the dependence of the equivalent thermal conductivity upon the sample thickness. This result, attribute d to radiative transfer, is confirmed by modelling. Radiative thermal conductivities are obtained with a Monte-Carlo code. Experimental and theoretical results are compared, It is demonstrated that the concept of effective conductivity is not relevant to these materials.