Exploring the Importance of Natural Convection Mechanism on Heat Transfer Response of Soil Medium in the Presence of an Unconfined Groundwater Flow

Soil thermal response is of great importance in thermally related geo-environmental practices such as contaminated soil thermal treatment and renewable energy storage systems. Despite previous studies showing natural convection influence on soil thermal response in hydrostatic conditions, less attention has been given to its effect in the presence of subsurface flow. Additionally, the few studies that considered this matter in their analyses explored that only in the presence of confined groundwater flow. Therefore, this study investigated the role of natural convection on soil thermal response in the presence of unconfined groundwater flow. A finite element model was developed in COMSOL Multiphysics to simulate hydro-thermal behavior of saturated soils. Results showed that, depending on the soil permeability and groundwater flow velocity, natural convection impact on soil thermal response can be significant. Moreover, results were interpreted using a non-dimensional number, known as mixed convection number, which considers the coupled effect of permeability and groundwater velocity. It was revealed that when mixed convection number increases, natural convection effect intensifies.