Effects of thermal properties of porous media on local thermal (non-)equilibrium heat transport

When analyzing convective heat transport, local thermal equilibrium (LTE) between the solid and fluid phases of water-saturated porous media is commonly assumed. However, experiments investigating the scope of validity of this assumption are lacking. We conducted heat transport experiments using two types of porous media having the same grain size (5 mm) but contrasting thermal properties (glass and polyoxymethylene) for different thermal Péclet numbers between 1.1 and 19.8. We used specifically crafted sensors to separately measure the temperature of the solid and fluid phases. Both LTE and local thermal non-equilibrium (LTNE) models were used to analyze the measurement data. While the LTE model was appropriate for all experimental conditions, small signatures of LTNE were detected. The experimental data and the sensitivity analysis using the LTNE model demonstrated that the volumetric heat capacity of solid plays a more significant role in causing LTNE than the solid thermal conductivity.