DEVELOPMENT OF A NOVEL METHOD FOR SURFACE TENSION MEASUREMENT: A DROP-BOUNCE METHOD

摘要

Thermophysical properties of liquid metals have important industrial usages in areas like casting, heat transfer, and containment designs, but are hard to obtain accurately because of contamination/reaction/evaporation at high temperatures. Advances in levitation techniques in recent years have made density, surface, and viscosity measurements more reliable, but each levitation technique still has its limitations. For ADL, one of the more versatile, compact, and easier-to-use levitation techniques, performing surface tension measurements is rather difficult under normal gravity conditions because of the lack of an equation to correct for the sample's imperfect spherical shape and rotation. The origin of this problem arises from the fact that to use ADL on the ground, an external force is necessary to levitate and excite the sample and obtaining detailed knowledge on how this force is applied to the sample is rather difficult. In order to overcome this problem, we developed a new drop-bounce method that can be used within the aerodynamic levitation system to measure the surface tension of reactive liquids. During the experiment, a levitated molten sample is dropped onto an inert substrate and the rebounded sample behaves as if under microgravity condition during its free fall and oscillation only in the 1=2 m=0 mode can be obtained. Fourier transformation of the oscillation pattern gives the resonance frequency of the 1=2 mode and allows us to calculate the sample's surface tension given its mass. Furthermore, a short experiment time less than 100ms dramatically reduced the chance of surface evaporation. Our measured surface tension data from 1417K to 2000K for gold has a standard deviation of 32.0 mJ/m~2 and agree well with published data by I. Egry conducted under microgravity conditions, with a maximum deviation of 1.7% between the two fitted linear equations. This shows that the drop-bounce method introduced in this study is a novel, reliable method for surface tension measurement with ADL and is successful in inducing the oscillation behavior of a spherical sample under microgravity conditions on the ground.