Evaporation induced solidification of cyclohexane drops under acoustic levitation condition
声悬浮条件下环己烷液滴的蒸发凝固

The evaporation process of a cyclohexane drop is investigated by single-axis acoustic levitation method. It is found that the evaporation of the cyclohexane drop results in the decrease of its temperature below the melting point, and leading to solidification. The real-time observation with a high speed camera shows that the cyclohexane nucleates near the equator of the drop surface and grows dendritically with an average velocity ranging from 12.5 to 160.4 mm/s. Further studies indicate that the ratio Sh/Nu of the average Sherwood number to Nusselt number under acoustic levitation condition is 1.3 times of that under natural convection condition. This suggests that the acoustic streaming boundary layer effectively strengthens the evaporation but has less promotion effect on the heat transfer. Therefore, the drop temperature declines to a lower value and the evaporation induced solidification occurs under acoustic levitation condition. Accordingly, a necessary condition for the occurrence of evaporation induced solidification of volatile liquids is proposed.