| Acoustic levitation (AL) is an important technique for containerless processing, which can be applied to containerless solidification of materials, contactless measurement of physical properties of liquids, and experimental investigation of free drops. The advantage of AL is its applicability to non-conducting substances and also to low-melting-point metallic materials. Due to the fact that the levitation capability of single-axis acoustic levitation (SAAL) is comparatively weak and its applications are mainly limited to low-density substances, this paper aims at enhancing the levitation capability of SAAL and realizing the containerless solidification of those materials with low melting temperature and high density.A two-cylinder model for SAAL incorporating BEM simulations is proposed, which introduces a factor concerning the geometric parameters of the levitator into the expressions for the time-averaged potential U, acoustic radiation force F, and restoring force constant Ki, respectively, and builds up the relationship between the levitation capabilities and the geometric parameters of a single-axis acoustic levitator. This model proves to be successful in predicting resonant modes of acoustic field and explaining the axially symmetric deviation of the levitated samples near the reflector and emitter.Concave reflecting surfaces of spherical cap, paraboloid and hyperboloid of revolution are investigated with regard to the dependence of the levitation force on the section radius Rb and curvature radius R (or depth D) of the reflector. It is found that the levitation force can be remarkably enhanced by choosing optimum value of R or D, and the possibility of this enhancement for spherically curved reflectors is the largest. The degree of levitation force enhancement by this means can also be facilitated by enlarging Rb and employing lower resonant mode. The deviation of the sample near the reflector is found likely to occur in circumstance of smaller Rb, larger D and higher resonant mode. The calculated dependence of levitation force on R, Rb and resonant mode is also verified by experiment and finally demonstrated to be in good agreement with experimental results.Single-axis acoustic levitation of the heaviest solid (iridium, p = 22.6g/cm3) and liquid (mercury, p = 13.6g/cm3) on the earth is achieved by greatly enhancing both the levitation force and stability through optimizing the geometric parameters of the self-developed single-axis acoustic levitator. This indicates that all the solids and liquids can be acoustically levitated on the earth in principle.The main influencing factors for containerless processing, such as the gas medium, gravitational levels, resonance adjustment, and temperature variations are studied. For a gas medium, the levitation force is determined not only by the ratio of its density to sound speed, but also by the ratios of its wavelength to the geometric parameters of the levitator. The increase of the gravitational level makes the levitation potential wells shallower or even disappearing. During the resonance adjustment, the sound pressuredistribution, levitation force and sample positions vary symmetrically with respect to the resonant state, and the allowed adjusting range of the reflector-emitter spacing is only the order of 0.005/1. In a quasi-static heating and cooling process, the resonant conditions, levitation force and threshold pressures pm (the minimum entrapping pressure) and pM (the maximum pressure to keep the integration of a liquid drop) are changed significantly. The temperature dependence of the first resonant spacing H\ comes mainly from the variation of wavelength, which is proportional to T1/2 The maximum levitation force FM has a drastic decreasing tendency with temperature rise due to its sensitivity to the geometric parameters/wavelength ratios. pm increases whereas pM decreases with the rise of temperature, which narrows the allowed pressure range for the safe and stable levitation of the processed drops at higher temperatures.The cond...
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