Effect of solute dispersion on thermal convection in a porous medium layer

Abstract

Thermal convection and overstable motions may sometimes play an important role in salt diffusion in an aquifer. In such cases hot saline water is in the deep layers of the aquifer, from which salt diffuses into the upper freshwater. Often the horizontal steady flow of the water in the aquifer increases the rate of diffusion of soluted materials. Salt diffusion is then characterized by the anisotropic dispersion tensor. The effects of salt dispersion by the steady state flow in the aquifer were examined in connection with the thermal stability of the flow field. It was found that dispersion of the soluted material reduces the stabilizing effect of the salinity profile but increases the stability of the flow field to pure overstable motions. Dispersion also changes the dimensions of Bénard cells in the porous medium. The dispersion tensor fluctuations hardly affect the stability criteria of the flow field but cause very small overstable motions that distort the shape of the convective current cells.