ISSN Online: 2377-424X
ISBN Print: 0-89116-909-1
International Heat Transfer Conference 9
WATER VAPOUR DIFFUSION AND THERMAL CONDUCTIVITY OF WET POROUS MEDIA
Resumo
With the help of the volume averaging method, this paper revisits the notion of thermal conductivity of a wet porous medium. Besides the definition of an average conductivity for a three-phase material, the enhancement of the heat transfer due to successive evaporation-condensation of water has to be taken into account. By considering only conductive heat transfer in each phase and vapour diffusion in gaseous phase, the average energy and vapour transport equations are deduced from the transport equations written at the pore scale. By means of a system closure, homogenized values of the transport coefficients are obtained. They are calculated for the one-dimensional and a two-dimensional periodic medium. The results are compared to the experimental ones. The agreement is qualitati-vely good at high moisture content. This analysis reconciles theory and experimental results because it demonstrates clearly that the apparent theoretical underestimate of the vapour flux is linked to a misinterpretation of the macroscopic parameters.