Abstract
The prediction of the thermal conductivity of soils is important in several phenomena related to ground. Among the practical applications at high temperatures are geothermal energy extraction, enhanced oil recovery, radioactive waste storage, ground heat pump and heat exchanger, forest fires and related problems. Some experimental results are available in the literature at temperatures in the range 30°C – 90°C. The theoretical model of the present paper assumes the unit cell of the porous medium as composed of a cubic space with a cubic solid particle at the center. The thermal conductivity of the porous medium is evaluated with the assumption of parallel isotherms. The water in the porous medium is distributed around the solid particle according to the phenomena of adsorption and capillarity. The thermal conductivity of the gas present within the pores takes into account the thermal conductivity of the water-saturated vapor and dry air without enhanced vapor diffusion and with the assumption of a linear variation of the relative humidity from zero water content to the field capacity. The predicted results, compared to the experimental data of soils at high temperatures show that the agreement is very good at moderate temperatures (30–50°C) and fairly acceptable at 70°C. At high temperature (90 °C) the predictions are somewhat higher than the experiments but a better agreement could be obtained decreasing the thermal conductivity of the water-saturated vapor. In any case the trend of the theoretical predictions is in very good agreement to the experiments also at high temperatures.
