Local Thermal Non-equilibrium Models in Porous Media: A Comparative Study of Conduction Effects

Abstract Instantaneous heat transfer between different phases, known as local thermal equilibrium (LTE), is commonly assumed for modeling heat transfer in porous media. This assumption may not hold in certain technical and environmental applications, particularly with large temperature gradients, large differences in thermal properties, or high velocities. Local thermal non-equilibrium (LTNE) models aim to describe heat transfer processes when the LTE assumption may fail. We compare three continuum-scale models from the pore to the representative elementary volume (REV) scale. Specifically, dual-network and REV-scale models are evaluated against a pore-resolved model used as a reference in the absence of experimental results. Different effective models are used to obtain upscaled properties on the REV scale and to compare resulting temperature profiles. The systems investigated are fully saturated, consisting of one fluid and one solid phase. This study focuses on purely conductive systems without significant differences in thermal properties. Results show that LTE holds for low interfacial resistances. However, for large interfacial resistances, solid and fluid temperatures differ. The REV-scale model with effective parameters obtained by homogenization leads to similar results as the pore-resolved model, whereas the dual-network model deviates more due to fixed spatial resolution. Among the evaluated REV-scale formulations, only the homogenization-based approach captures the LTNE behavior, as it incorporates the interfacial heat transfer coefficient. Our results provide a basis for conduction-dominated heat transfer in saturated porous media and for further systematic comparisons that incorporate convection relevant to a broader range of applications.