Predictions of thermal characteristics for mixed porous media

To investigate the overall thermal conductivity characteristics for composites of two dry porous materials, an experiment was conducted to measure the thermal conductivities for mixtures of fine sand and white lime, fine sand and coal powder, and salt and sawdust at various volumetric mixing fractions using a transient line-heat-source device. Results indicated that the low-thermal-conductivity material has a pronounced influence on the heat-conduction process in the composite and the overall thermal conductivity does not obey a simple mixing law. The concept of basic heat-transfer routes was introduced to physically describe the heat-transfer mechanism. A probability-based group-contribution theory was used to obtain an empirically adjusted theoretical equation. This equation fit measured data with an R² of 0.96 or better, with a significance level of 0.001. The general effective media (GEM) equation based on the effective media and percolation theories was also used to describe the experimental data.