Nucleation mechanism of nanofluid drops under acoustic levitation

In this study, 0.03 wt% graphene oxide nanofluid was prepared by adding graphene oxide nanosheets into deionized water, and nucleation experiments were conducted with levitated deionized water and graphene oxide nanofluid drops to study their supercooling degree distributions and nucleation mechanism. Results show that the supercooling degree of the nanofluid drop is significantly less than that of the deionized water drop, and that supercooling degree increases as ultrasonic power increases. The nucleation rates of the deionized water and nanofluid drops at two ultrasonic power levels was obtained according to the statistical nucleation theory, and heterogeneous nucleation factors and nucleation sites were calculated based on the classical nucleation theory. The nucleation rate of nanofluid is greater than that of deionized water at the same supercooling degree. The analysis of the heterogeneous nucleation factors revealed that levitated deionized water and nanofluid drops exhibit heterogeneous nucleation, and that heterogeneous nucleation factor decreases as ultrasonic power increases. The effects of ultrasonic power and nanoparticles on nucleation are coupled to each other. Comparing the nucleation site of drops at two power levels showed that the levitated deionized water drop exhibits surface dominated nucleation and the levitated nanofluid drop exhibits both surface-and volume-dominated nucleation behaviors, which are affected by ultrasonic wave. Additionally, the surface nucleation site increases as ultrasonic power increases. (C) 2017 Elsevier Ltd. All rights reserved.