Evaporation in a presence of a dissolved salt is important in relation with various applications such as the conservation of our cultural heritage, the injection of CO2 in saline aquifer or the soil salinization problem, to name only a few. The problem is made particularly interesting by the crystallization of the salt resulting from the evaporation process. Here we are interested in situations where the salt crystallizes at the surface of the porous medium and forms crystallized salt structures referred to as efflorescence. Although advances have been made in recent years on the understanding of the factors controlling the formation and growth of efflorescence, many questions are still open. Here we are interested in the impact of efflorescence on the evaporation kinetics of the porous medium. udThe study is based on drying experiments in the presence of dissolved sodium chloride. By varying the average size of the beads forming the porous medium, we show that the formation of the efflorescence does not affect significantly the drying process and can even enhance the drying rate when the beads are sufficiently large. By contrast the efflorescence can greatly affect the drying process and even blocks the evaporation process for sufficiently small beads. We therefore show the existence of a transition between the two regimes, namely the blocking regime and the enhanced drying rate regime. It is shown that the two regimes correspond to two different types of efflorescence, referred to as crusty and cauliflower (or patchy) respectively. Then by varying the initial salt concentration for a given bead size, we show that the interplay between drying and the efflorescence formation leads to a non-monotonous variation of the drying rate with the initial salt concentration when the efflorescence is patchy but not when the efflorescence is crusty. This has to do with a porous medium “coffee ring” effect due to evaporation fluxes higher at the periphery of the sample. ud
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机译：在溶解盐的存在下进行蒸发与各种应用（例如保护我们的文化遗产，向盐水层中注入CO2或土壤盐碱化问题）很重要。通过蒸发过程中产生的盐的结晶使该问题特别引起关注。在这里，我们对盐在多孔介质表面结晶并形成结晶的盐结构（称为风化）的情况感兴趣。尽管近年来在了解控制风化形成和生长的因素方面已取得进展，但仍有许多问题尚待解决。在这里，我们对风化对多孔介质蒸发动力学的影响感兴趣。这项研究是基于在溶解的氯化钠存在下的干燥实验。通过改变形成多孔介质的珠粒的平均尺寸，我们显示出风化的形成不会显着影响干燥过程，当珠粒足够大时，甚至可以提高干燥速率。相反，对于足够小的珠子，风化会极大地影响干燥过程，甚至阻碍蒸发过程。因此，我们显示了两种状态之间存在过渡，即阻塞状态和增强的干燥速率状态。结果表明，两种处理方式对应于两种不同类型的风化作用，分别称为硬壳和花椰菜（或斑片状）。然后通过改变给定珠粒大小的初始盐浓度，我们发现干燥和风化形成之间的相互作用导致风化呈片状而不是风化时干燥速度随初始盐浓度的非单调变化。很硬这与多孔介质的“咖啡环”效应有关，这是由于样品外围的蒸发通量更高。 ud
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