In-situ observation and detection of the dynamic crystallization in acoustically levitated droplets

In this paper, visual experiments were carried out to study the NaCl crystallization process in acoustically levitated droplets. Image processing was employed to acquire the evaporation rate of the droplets and PIV analysis was used to characterize the flow filed. Effects of droplet size and initial NaCl concentration were investigated, and the crystallization behaviors in the levitated droplet and surface droplet were compared. The results indicate that the acoustic filed introduced a forced convection of fluid within the levitated droplets, influencing the evaporation rate, supersaturation degree and the morphology of the crystal product. The obtained mechanism is important to the application of acoustically levitated droplet and can be further applied to other crystallization research based on the acoustic levitation systems.