Sodium chloride crystallization in a model porous medium during drying with a receding sharp front

Abstract

Visualization experiments in a model porous medium are presented in this work to study the interplay between salt precipitation and gas–liquid displacement during evaporation for the drying situation characterized by a receding sharp drying front. Various types of salt subflorescence are distinguished depending on the location of the subflorescence growth, namely, away from the drying front in the region predominantly occupied by gas or in the liquid-saturated region. A distinction is also made regarding the subflorescence that develops in the predominantly gaseous region depending on the degree of occupation of the pores by the subflorescence structure. The experiment confirms that the capillary liquid films can be a pathway for the dissolved salt transport. As a result of the capillary film effect, the evaporation front must be distinguished from the drying front and subflorescence structures can develop in the vicinity of the evaporation front away from the drying front. It is also shown that the pinning of the evaporation front leads to an anomalous drying front kinetics with a drying front position varying linearly with time and not according to the classical scaling with the square root of time.