Heat flow’s propagation within a porous medium: analogical and numerical modeling

Determining the thermal characteristics of geologic media has numerous applications for low enthalpy geothermal systems design and monitoring. Despite the interest in the topic, there appears to be a scarcity of experimental data in this respect, most of the thermal properties evaluations being based on numerical simulations and back analysis on few real data. Therefore analogical and numerical modeling of heat flows in an ad hoc designed thermal box are presented here. The designed thermal box is a low cost apparatus, easily implementable in most laboratories that conversely allow for accurate heat propagation measurements. Tests performed under different saturation degrees and under induced water fluxes were analysed to evaluate the effect of moisture content on the heat propagation and the relative amounts of conductive and convective phenomena into the medium. Cumulative multiple-impulse tests were also carried out in order to evaluate the heat storage capacity of the material. Analogical data processing confirmed that the heat induced propagates faster from dry to saturated conditions but is less dependent on intermediate water contents. A stronger increase in the heat propagation velocity was obtained introducing a water flow effect. Numerical simulations performed with OpenGeoSys code reached a good agreement with experimental data, enabling to evaluate the accuracy of the lab tests, to understand in detail the behaviour of the medium at different saturation degrees and to obtain more reliable thermal characteristics. Coupling laboratory measurements with numerical modeling seems to have good potentiality as a reliable and accurate tool for thermal property assessment.