Treatment of transient heat transfer among fluids and particles in free aquifers

Abstract

Recently the impetus towards use of aquifer as thermal storage systems has increased. Since the surface of free aquifers fluctuates irregularly due to both inflow and outflow of groundwater, treatment is difficult compared with the case of confined aquifers. In the case of free aquifers, non-equilibrium heat transfer between fluid and particle phases exerts much influence. Even in confined aquifers, the unsteady heat transfer is marked under marble or gravel-component. The inherent properties of soils are dismissed and part of them are reflected poorly in apparent properties such as equivalent heat capacity or conductivity. Therefore, even superficial velocity has been wrongly estimated. In this paper, a two-phase model is introduced for consideration of heat propagation even into the particle phase. Then, the effectiveness of the model is confirmed using a laboratory test apparatus in two dimensions. Finally, significant deviations of temperature propagation by the particle sizes are simulated.