A simple two-phase approach to predict moisture-dependent thermal conductivity for porous materials

This study develops a generalized solution for moisture-dependent thermal conductivity (2eff) in porous media, utilizing readily available parameters. By introducing arbitrary dry and saturated phases, the tri-phase model (solid, gas, and water) is simplified into a two-phase model. Seven analytical solutions are adapted, including series-parallel, Maxwell-Eucken, Landauer's, exponential, and Somerton's relations. The proposed method requires only two parameters to predict 2eff under different degrees of saturation (Sr): effective dry thermal conductivity (2dry, where Sr = 0) and effective saturated thermal conductivity (2sat, where Sr = 1). In the absence of direct 2sat measurement, this 2sat can be obtained using 2dry and the parallel relation for highly porous media, and using Landauer's relation for medium-density materials. Validation results indicate that both Landauer's and exponential relations provide the upper bound and lower bounds, respectively, for 2eff. For medium-density materials, the upper bound aligns with the parallel relation and the lower bound aligns with Landauer's relation.