LABORATORY ESTIMATION OF APPARENT SOIL THERMAL CONDUCTIVITY USING A NUMERICAL APPROACH

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Abstract
The experimental equipment used in the laboratory is a metal cylinder with its top and its base, containing a soil sample. A sensitive temperature probe is placed at the center of the soil, and temperature data are recorded versus time during a transient heat flow. The estimate of the thermal conductivity is provided according to a numerical approach for solving the heat conduction equation, using the finite element method. This numerical approach takes into account the heat transfer in all the components of the apparatus (metal wall, porous medium, temperature probe, and its wire) and in all directions (axial and radial fluxes). Comparing calculated values and experimental data gives a criterion that shows how the modeling fits. We first present numerical and experimental results from isotropic soil samples. The chosen modeling fits very well, and we regard estimated values of thermal conductivity as satisfactory. Secondly we present a theoretical and numerical approach to calculating two thermal conductivities for an anisotropic soil (thermal conductivities in the radial and axial directions). For this purpose, we combine the finite element method with a nonlinear fitting method and show that two temperature probes are needed in the soil sample, and that their locations are optimized according to numerical simulations.

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