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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. more...

Graphene oxide nanosheet is considered as an excellent additive owing to desirable thermal conductivity and hydrophilicity. Graphene oxide nanofluids were prepared by adding graphene oxide nanosheets into deionized water under ultrasonic oscillation. Particle size distributions were measured by Laser Size and Zeta Potential Analyzer. Nucleation rates and supercooling degrees of deionized water and graphene oxide nanofluids are investigated using classical nucleation theory. Deionized water nucleates homogeneously, but graphene oxide nanofluids involve homogeneous nucleation of inside deionized water and heterogeneous nucleation arising from graphene oxide nanosheets. Our theoretical analysis shows that two types of nucleation in graphene oxide nanofluids can differ by 23.08 orders of magnitude at 241.65 K. Therefore, nucleation rate mainly refers to the heterogeneous part. The heterogeneous nucleation rates are obtained by integrating the particle size based on the probability density functions and particle size distributions fitted via MATLAB. The supercooling degree of deionized water is approximately 31.5 K, whereas the supercooling degrees of four different concentrations of graphene oxide nanofluids are 7.98, 7.93, 3.05, and 3.03 K. The supercooling degrees were reduced by more than 74% with the corresponding increase in volume concentration. Therefore, graphene oxide nanofluids can be used as alternative phase change materials in cold storage application because of their low supercooling degrees. more...

Acoustic levitation constitutes an alternative experiment technology for avoiding contamination from container walls or other external objects. Graphene oxide nanofluid drop was acoustically levitated and solidified, and supercooling degree of nanofluid drop at different cooling temperatures was measured. The supercooling degree of nanofluid drop can be reduced by 59.79% in comparison to that of the deionized water, and the reduction of supercooling degree gradually weakens with the decrease of cooling temperature. Based on Wenzel's wetting model, the authors established a new physical model of nanosheet to analyze the effect of rough surface on the nucleation behavior and supercooling degree, revealing that only on the upper or lower surfaces of the nanosheets can crystal nucleus form and grow, and nucleation on the thickness surface is difficult. Furthermore, a model for predicting nucleation rate of nanofluid was proposed, suggesting that the nucleation rate increases significantly with the increasing of supercooling degree. more...

Points out the obvious deficiencies in capture/playback mechanism at present, aiming at difficulties of maintenance and extension in constantly altered GUI elements, presents a new GUI automation testing solution—Building AUILibrary. It can search, identify all the controls, trigger all kinds of mouse and keyboard events, execute data driving verification roundly and accurately, trace and record execution process and save the locale when exception occurs, implement flexible and effective GUI automation testing indeed. more...