THERMAL CONDUCTIVITY OF TWO POROUS MEDIA AS A FUNCTION OF WATER CONTENT, TEMPERATURE, AND DENSITY

Abstract

Appropriate values for the thermal conductivity, which include the contribution of vapor transfer, are required to describe heat transport in a porous medium. We measured the apparent thermal diffusivity of a glass bead medium and a Norfolk sandy loam (Typic Paleudult) as a function of water content and temperature. The thermal conductivity, .lambda., was determined from the thermal diffusivity and the heat capacity of the media. We also calculated values for .lambda. with the de Vries model. This paper presents a summary of the de Vries equations and values of the parameters pertaining to the porous media studied. Results show that the de Vries model can be used satisfactorily to calculate the thermal conductivity, because the measured and calculated values were within 10%. In addition, expressions of thermal conductivity presented were not only a function of water content and temperature, but also of bulk density. We found that the measured .lambda. for the loamy sand was consistently larger than the calculated .lambda. at intermediate water contents and near saturation. Calculations indicated that the differences were probably caused by enhanced vapor diffusion in the intermediate water content range and by convective heat transport in the liquid phase at the higher water content values.