Evaporation with sodium chloride crystallization in a capillary tube

• Evaporation of a sodium chloride solution triggers crystallization.
• The local salt concentration field is computed from numerical simulations.
• Crystallization occurs only when a supersaturated state is reached.
• Salt concentration varies spatially.
• Crystal growth is first controlled by reaction kinetics and then by transport.

Sodium chloride crystallization induced by evaporation of aqueous solution is studied from visualization experiments in a circular capillary tube. In agreement with recent studies, the onset of crystallization is observed with a significant supersaturation. Detailed information on the precipitation kinetics and transport of ions is obtained from numerical computations of the ion mass fraction field during the evaporation process. It is shown that the precipitation kinetics is fast compared to transport so that the crystal growth is mostly controlled by the transport. This offers possible simplifications for analyzing more involved situations such as crystallization in porous media. The fact that the significant supersaturation does not lead to tube damage is explained.