Evaporation Characteristics of Sessile Brine Droplets Under Low Pressure

In this paper, the evaporation characteristics of sessile brine droplets in a low-pressure environment are studied experimentally and theoretically. Regarding the experiments, a visual system was established, and the contact angles and contact diameters of the sessile brine droplet during its evaporation process were obtained at low-pressure conditions. A weighing sensor was employed to record the changes in droplet mass. In terms of the theory, a heat and mass transfer model for the evaporation of sessile brine droplets at low-pressure conditions was established. The surface curvature of the droplet and the activity coefficient during its evaporation process were considered. By comparing with experimental results, the reliability of the model has been verified. The results showed that when the crystal morphology of the brine droplets no longer changed, there was still some water that did not evaporate from the crystal gaps. As evaporation proceeds, the contact angle of brine droplets decreases continuously, and the lower the pressure, the faster the contact angle decreases. The precipitated crystals will suppress the spreading and contraction of the contact line, causing the contact diameter to no longer change. The higher the salt concentration of the droplet, the slower the evaporation rate. The lower the ambient pressure, the faster the droplet evaporation rate. Compared to flat surfaces, droplets on convex substrates have a larger spreading area, resulting in a faster evaporation rate.