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

• A two-phase model is proposed to predict moisture-dependent thermal conductivity. • Prediction based on effective dry and saturated thermal conductivity. • Landauer's and exponential relations form bounds for highly porous materials. • Landauer's and parallel relations form bounds for medium-density materials. This study develops a generalized solution for moisture-dependent thermal conductivity (λ eff ) 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 λ eff under different degrees of saturation (S r ): effective dry thermal conductivity (λ dry , where S r = 0) and effective saturated thermal conductivity (λ sat , where S r = 1). In the absence of direct λ sat measurement, this λ sat can be obtained using λ dry 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 λ eff . For medium-density materials, the upper bound aligns with the parallel relation and the lower bound aligns with Landauer's relation.