Series-parallel resistance method based thermal conductivity model for rock-soil with low or high porosity

The estimation of the underground rock-soil thermal conductivity from different depths is of great importance for the studies on the performance prediction and evaluation of geothermal utilization systems. Based on the authors' previous work on the prediction of rock-soils with moderate porosities (0.2146 < n < 0.4764), this study presents a series-parallel thermal resistance method based thermal conductivity model for the rock-soils with different constituents and water contents at low (n < 0.2146) or high porosity (n > 0.4764). The arrangement of different phases in the cubic cell element is introduced, and the thermal resistance for each part is theoretically derived to achieve the expression of the effective thermal conductivity. After verified by 74 experimentally measured and predicted results of rock-soil sample thermal conductivities in the existing work, the newly proposed method is validated to be successful to predict the rock-soil thermal conductivity with an average RMSE of 0.1289, which implies that the present model configured with two hemispheres and cylindrical water framework and based on the series-parallel resistance method provides an accurate prediction on the thermal conductivity of the rock-soils with different constituents and water contents at low or high porosity.