Prediction of effective thermal conductivity of moist wood concrete

Abstract

From the set of existing models available for predicting the thermal conductivity of porous materials such as soils, building materials, etc. two models based on two different approaches have been selected in order to estimate the thermal conductivity of moist wood concrete. The first model is based on the strictly mathematical solution to the heat conduction equation using a continuous medium approximation. The second employs the Ohm's law approach. Besides the characteristics of the various phases, such as each phase's thermal conductivity and its volume fraction, both the Pande and Gori and the Jackson and Black models take into account the geometrical arrangement of the particles by introducing a morphological parameter such as the coefficient of effective continuous medium, P and the stereological concept of contiguity, respectively. A new parameter named the liquid-liquid contiguity has been introduced to preserve the validity of the model as proposed by Jackson and Black for saturation greater than 0.9. Based on the same electrical analogy as Jackson and Black, an expression for calculating the effective thermal conductivity of unsaturated material has been proposed. A new coaxial thermal probe, developed at the LTHE (France), has been used for measuring thermal conductivity at various moisture contents. One original feature of the corresponding probe is its very low mass by unit length - less than 10 g m-1. It allows for taking measurements even if the thermal contact is very poor. Calculated values of the effective thermal conductivity of these materials have been compared with experimental measurements. These models are found to yield predictions which agree quite closely with experimental data for wood concrete for different amounts of wood aggregates and saturation degrees.