Dynamics of solute transport in capillary tubes delineated by dual energy imaging

Saline water evaporation from a single meniscus plays an important role in determining the general dynamics of evaporation from porous media filled with saline water, which is relevant to several processes such as soil salinization, land-atmosphere interaction and soil moisture-precipitation interactions. Fundamental understanding of the mechanisms controlling solute transport and deposition in single capillary tubes is a necessary step to describe saline water evaporation and solute precipitation in complex porous media (Norouzi Rad et al., 2013; Shokri-Kuehni et al., 2017a; Shokri-Kuehni et al., 2017b). Within this context, we utilized dual energy imaging using synchrotron X-ray micro-tomography (Shokri-Kuehni et al., 2018) to investigate solute transport and deposition during evaporation from single capillary tubes of square and circular cross sections with lateral dimension of 1 mm and 3 mm (two sizes per cross section which resulted in four capillary tubes in total). The capillary tubes were filled with CaI2 solution of 5% concentration (by weight) and were placed under similar evaporative conditions. All boundaries were closed except top which was exposed to air for evaporation. The drying capillary tubes were scanned approximately once every hour for nearly 20 hrs. The recorded images enabled us to quantify solute concentration with a high spatial and temporal resolution throughout the capillary tubes with different sizes and cross sections and delineate the key transport mechanisms controlling solute transport and preferential deposition during evaporation. Our findings clearly show the contribution and impact of corner flow observed in square capillary tubes on the spatio-temporal distribution of solute, the evaporative mass losses and the velocity of the receding meniscus. The obtained results extend the fundamental understanding required for describing the transport mechanisms controlling saline water evaporation from porous media.

References

Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Phys. Rev. E, 88, 032404.

Shokri-Kuehni, S.M.S., T. Vetter, C. Webb, N. Shokri (2017a), Geophys. Res. Lett., 44, 5504–5510.

Shokri-Kuehni, S.M.S., M. Norouzirad, C. Webb, N. Shokri (2017b), Adv. Water Resour., 105, 154-161.

Shokri-Kuehni, S.M.S., M. Bergstad, M. Sahimi, C. Webb, N. Shokri (2018b), Sci. Rep., 10, 10731, London: Nature Publishing Group.