Abstract
AbstractEvaporation of saline water from porous media and associated salt deposition are important for many applications ranging from soil salinization to the protection of archeological and civil structures. We investigate the effects of textural heterogeneity of porous media on evaporative salt precipitation patterns. Textural heterogeneity has been introduced into sand columns to form capillary‐interacting porous domains comprised different particle sizes. Several levels of textural contrasts were experimentally studied in terms of their effects on drying rates, salt precipitation patterns, and drying front displacement rates. Results show that in contrast with evaporation of pure water, evaporation of saline solutions from media with textural contrasts exerted only a minor effect on evaporation rates. This difference is attributed to enhanced liquid transport within the highly porous precipitated salt on the surface. The presence of textural contrasts significantly enhanced preferential spread of salt precipitation on the surface. The enhancement is attributed to low surface water content of the coarse domain and larger spacing between remaining evaporating wet pore clusters in which greater local evaporation rates are accelerating salt precipitation. The study illustrates the interactions between the water characteristic curve, preferential drying front displacement and subsequent salt deposition patterns, as also seen in high resolution X‐ray Computed tomography (CT) used to verify the suggested mechanisms. The study provides new insights into mechanisms of saline water evaporation and the complex effects of porous media heterogeneity on salt precipitation patterns and dynamics; all critical ingredients for enhanced understanding of the salt distribution in and transport in soils.
Highlights
Saline water evaporation from porous media and salt precipitation affects water management, soil and groundwater salinization, and various other environmental processes [Jardine et al., 2007; Prasad et al, 2010; Xiao et al, 2011; Russo, 2013]
Evaporation experiments were conducted in an environmental chamber at constant temperature of 30°C and relative humidity (RH) of 30%
As the salt begins to precipitate and expand over the surface, the active evaporation surface is extended to the exterior of the precipitation layer and the evaporation rate is controlled by the pore-scale dynamics of the salt precipitation, which is considered
Summary
Saline water evaporation from porous media and salt precipitation affects water management, soil and groundwater salinization, and various other environmental processes [Jardine et al., 2007; Prasad et al, 2010; Xiao et al, 2011; Russo, 2013]. Natural soils may contain various types of layers, textural contrasts and material interfaces that reflect depositional and scouring processes, refilling of cracks formed during freezing and thawing or swelling and shrinking cycles, and the interception of Aeolian dust and other local plant alterations The presence of such porous media discontinuities induces spatially abrupt changes in the capillarity and flow properties, and modify transport processes as reported in several studies [Pillai et al, 2009; Lehmann and Or, 2009; Nachshon et al, 2011; Veran-Tissoires et al, 2012; Bechtold et al, 2011, Bergstad et al, 2017]. Motivated by the important impacts of the presence of heterogeneity on precipitation dynamics in porous media, we seek to quantify how capillarycoupled porous interfaces and their characteristics affect salt precipitation patterns and evaporation dynamics of saline solutions by performing a series of well-controlled drying experiments at the macro- and micro-scale
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