Some Observations on the Impact of a Low-Solubility Ionic Solution on Drying Characteristics of a Model Porous Medium

Abstract

We study the impact on the drying rate, of the presence of suspended elements, such as calcium sulfate ions with a low solubility, in the interstitial fluid of a porous medium. In order to single out this process in the complexity of a porous medium, we study it through drying in a simple capillary exhibiting characteristics such that it reproduces some critical aspects of drying of porous media. Another specificity of our work is that we focus on the evaporation of initially ion saturated solutions. We first show that in such a capillary the drying process varies depending on the wettability characteristics. Typically the drying rate is much smaller with hydrophobic surfaces because of the airliquid interface which tends to withdraw inside the medium, while for hydrophilic surfaces there remains a continuous liquid film up to the entrance. Then it appears that an ionic solution dries slower than a pure liquid, because the crystals formed along the capillary walls tend to induce a dewetting of the capillary entrance, pushing inwards the first liquid-air interface from which most of the evaporation occurs. An experiment with a model colloidal suspension further illustrates this mechanism: the accumulation of solid particles along the wall forms a deposit which pushes inwards the first liquid-air interface from which evaporation takes place. Finally we look at the impact, on the drying characteristics, of the presence of different additives in the ionic solution.

Wetting equilibrium in a rectangular channel

“…1). This is in contrast to a later study by Seck et al 12 In this case, the rectangular channel was nearly perfect, and very thin fluid columns were observed (right column in Fig. 1).…”

“…The value of s* given by eqn (36) is s* C 0.018, again this is consistent with the observation in ref. 12 (also see the right column of Fig. 1).…”

“…In the experiment of Seck et al, 12 the aspect ratio is b = 0.2 and the cross-section is nearly perfect rectangle, so a is very small. In this case, Fig.…”

Drying of a Compressible Biporous Material

“…Such a connection is indeed necessary to ensure a constant drying rate [30]. Although here the shape of the hydraulic network is more complex, the drying process observed is finally similar to the drying of a single channel (filled with liquid) taking the form of a progressive penetration of a large air finger leaving liquid films behind along some channel walls [24,31,32]. In that case the CRP lasts as long as the liquid films exist and can transport liquid sufficiently rapidly with regards to the rate of evaporation imposed along the sample free surface.…”

Editorial: Saline Water Evaporation from Porous Media

“…Their analysis provided us with a better physical understanding of the damaging effect of in-pore crystallization of thenardite and halite during drying of porous building materials. Seck et al (2018) investigated the impact of the presence of suspended elements such as calcium sulfate ions on the drying characteristics. They used a single capillary for evaporation experiments capable of reproducing some critical aspects of drying of porous media.…”