Two-phase pore-network model for evaporation-driven salt precipitation -- representation and analysis of pore-scale processes

Abstract: Evaporation-driven salt precipitation occurs in different contexts and leads to challenges in case of e.g. soil salinization or stress-introducing precipitation in building material. During evaporation, brine in porous media gets concentrated due to the loss of water until the solubility limit is reached and salt precipitates. Different models on the REV-scale are available, which describe the effective behavior of the system. But several studies indicate that the controlling processes of evaporation-driven salt precipitation act on the pore scale. Thus, pore-scale models are necessary for a detailed understanding. In this paper, we present a dynamic, two-phase, non-isothermal pore-network model for evaporation-driven salt precipitation. Salt precipitation is modeled with a kinetic reaction and the resulting pore-space alteration is considered. Further, the model includes influence of the salt concentration on the fluid properties and liquid corner films. The capabilities of the model are demonstrated in several numerical evaporation experiments. The model is able to represent the effects of the decrease of pore space due to precipitation on the flow, phase displacement and salt transport. Further, the influence of the location of the brine-air interface and its dependency on the presence of liquid corner flow is described. Additionally, pore-scale heterogeneities and their effects like capillary pumping can be modeled. All these pore-scale effects have an influence on the salt precipitation process and the global behavior of the porous system. The presented model provides a general tool for further investigations of salt precipitation on the pore scale and transfer to the REV scale.