The Influence of the Darcy Velocity of Groundwater Flow on the Effective Thermal Conductivity

Abstract

An extensive database of groundwater influenced geothermal systems was developed through experimental investigation with a conduction and convection laboratory device. The experimental investigation focused on groundwater flow velocities and thermal loads with practical relevance, thereby acting a reasonable extension for the currently available measuring data concerning groundwater flow influenced geothermal systems. The transferability of the database to in-situ geothermal systems was proved via experimental investigation in two geothermal field testing sites. By the means of a numerical model, which was calibrated and validated with the experimental database, an extension of the experimental investigation range of middle to coarse sand was stretched out to cover silt, fine sand and gravel. With the aid of this database, recommendations on the dimensioning of geothermal systems influenced by groundwater were developed. The correlation between the increase of the effective thermal conductivity of sands and the groundwater flow velocity was quantitatively determined and summarized in a tabular form for weakly aquiferous, aquiferous and strongly aquiferous sands. Therefore, it is possible to distinguish by practical engineering means between the effective thermal conductivities not only for dry, moist and water-saturated sand - according to common literature and national standards - but also for weakly aquiferous, aquiferous and strongly aquiferous sands, which in return contributes to the development of renewable energies.