Double‐diffusive convection in groundwater wells

Abstract

Double‐diffusive convection caused by variations in solute concentration and temperature within a fluid body has previously been studied in connection with oceanic mixing processes, astrophysics, metallurgy, geology, and vadose zone hydrology but has not previously been studied in connection with thermohaline transport in a groundwater well. This paper considers whether double‐diffusive convection induced by salinity and/or temperature variations is a plausible mechanism for heat and solute transport in a groundwater well. This is examined theoretically using Rayleigh number stability “onset” criteria for fluid in a cylinder that considers the cylindrical well geometry and geothermal/solute boundary conditions. Theoretical results suggest that both monotonic and oscillatory double‐diffusive convection are plausible transport phenomena in groundwater wells. These analyses have important implications for hydrogeology because they provide another theoretically plausible mechanism by which heat and solute may mix in a well. This previously unaccounted for thermohaline mixing phenomenon may therefore be critical in the interpretation of well hydrogeologic and hydrochemical data.