A CFD Study Assisted with Experimental Confirmation for Liquid Shape Control of Electromagnetically Levitated Bulk Mater
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AFTER the development of the past century, the electromagnetic levitation (EML) technique is playing an important role in the materials science field.[1–3] Many thermophysical properties of various alloy systems in the overheated or undercooled state can be accurately measured by this method.[4,5] Meanwhile, with the help of the containerless environment,[6] the solidification mechanism under unconventional or extreme conditions can be systematically studied. The characteristics of noncontact electromagnetic control make it possible to accelerate the discovery of new materials. Recently, EML with bulk metallic materials has become the research frontier of this technology, which has many merits such as the larger sample size, richer performance characterization methods, and wider X. CAI, H.P. WANG, M.X. LI, Y.H. WU, and B. WEI are with the Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 1, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
application in industry. In regard to EML with bulk metallic materials, the problem of levitating bulk solid metallic samples can be solved using an optimized levitator structure and excitation parameters. However, when the metallic sample is heated to the liquid state, the free shape of the melt is determined by the combined results of gravity, surface tension, and electromagnetic and viscous forces. In addition, due to the additional electromagnetic stirring within the melt, the drastic flow becomes an unstable factor in levitation experiments and can seriously deteriorate the performance of the electromagnetic levitation process. Therefore, the levitation of a bulk melt is a difficult task during materials processing. For this issue, numerous fruitful studies have been conducted to investigate the melt behavior in high-frequency electromagnetic fields. Most samples are less than 1 g in mass and less than 6 mm in diameter.[7,8] The levitated sample in the experiments has an approximately spherical shape that can be fitted by Legendre polynomials. This approach can be used to determine the sample density. The early EML experiments can be traced back to the 1950s when Okress[9] made a cone-shaped coil to levitate aluminum in the air, and a melt with a cone shape was observed in experiments.
Recently, a series of space experiments have been performed to explore the influence of convection on the multiphase solidification process.[10] In addition, ground-based EML experiments have achieved the levitation of materials up to 500 g.[11] Due to the complex melt environment with high-temperature, completely opaque, easily reactive, and noncontact characteristics in EML experiments, it is difficult to collect detailed information about the flow within melts by conventional detection methods. Therefore, as the supplement to the experimental approach, the fluid dynamics of liquid metals in an alternating electromagnetic field have been investigated by various numerical simulation methods.[12
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