Evaporation modes of LiBr, CaCl2, LiCl, NaCl aqueous salt solution droplets on aluminum surface

Abstract

The evaporation of droplets of the LiBr, CaCl2, LiCl and NaCl aqueous salt solutions were studied experimentally and their evaporation characteristics were compared to droplets of distilled water. The geometrical parameters of droplets (contact angle, height, and diameter) were measured using three methods of data processing: tangential methods (T) and the Young-Laplace method (Y-L). Scattering of the measured data does not depend on the processing method selected for large contact angles. However, in the case of small contact angles, the Y-L method exhibited the smallest measurement error. An optical method allowed for measuring the contact angle of salt solutions droplets just prior to crystallization. The experiments have shown that crystalline hydrates grow near the contact line and distort the droplet profile. The contact angles of salt solution droplets were found to depend on time in a non-linear manner. Typical evaporation modes of the studied aqueous salt solutions are detected: 1 – increasing the contact diameter; 2 – pinning the droplet; 3 – formation of salt crystals (NaCl) or crystalline hydrates (LiBr, CaCl2 and LiCl).