Nonlinear effects of salt concentrations on evaporation from porous media



[1] Evaporation from porous media saturated with salt solution is influenced by the interactions among the transport properties of porous media, thermodynamics of the evaporating solution and environmental conditions. To study the effects of salt concentrations on the evaporation dynamics, we conducted a series of evaporation experiments under constant atmospheric conditions using columns packed with sand particles saturated with various NaCl solutions differing in concentrations. Results show that the evaporation rate decreases as NaCl concentration increases only up to a certain level. When exceeding this level, any further increase of NaCl concentration results in higher evaporation rates which is described theoretically using the thermodynamics of the solution. Results also reveal a nonlinear relation between NaCl concentrations and onset of efflorescence which is described by the numerical solution of the classical convection-diffusion equation. Moreover, we found a strong correlation between the growth dynamics of precipitated salt at the surface and the evaporation rate such that the maximum rate of surface coverage by salt coincide with the end of stage-1 evaporation. This potentially offers a new method to nondestructively study the evaporation process from saline porous media.