Effect of processing conditions on drop behavior in an electromagnetic levitator
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INTRODUCTION
SINCE the first patent in 1923 by Muck[1] in Germany, the electromagnetic levitation (EML) technique has become a widely used experimental technique for the processing of molten metals,[2] in which the shape and position of the molten metals can be controlled without a container. As the molten sample can be free from contamination and heterogeneous nucleation at the container wall, this containerless technique is suitable for experiments which need an extremely clean environment or an undercooled molten sample, such as the purification of metals, homogenization of alloys, and so on. Also, besides such metal processes, the EML technique has been utilized in the measurement of thermophysical properties of high-temperature molten metals and semiconductors such as surface tension, density, and viscosity.[3–9] Recently, The Second International Microgravity Laboratory (IML-2) experiments using TEMPUS (Tiegelfreie ElektroMagnetische Positionierung Unter Schwerelosigkeit) were also attempted in the microgravity environment.[10,11,12] Consequently, the thermophysical properties could be measured over a wide temperature range, including the undercooled condition, without any possible contamination. With the above experimental studies using the EML technique, and after the pioneering work by Okress et al.,[13] many extensive theoretical studies have been carried out to quantitatively understand the phenomenon of electromagnetic melting. The analyses of EML are divided into the following three aspects: (1) analysis of the electromagnetic field to predict the lifting force and the power absorption in the molten metal drop, (2) analysis of the temperature and flow fields in the drop due to the electromagnetic force, and (3) analysis of the deformation of the drop shape caused by the electromagnetic force. Most of the previous literature has been concerned with one or more of these S.H. HAHN, Postdoctoral Fellow, Y. SAKAI, Student, T. TSUKADA, Associate Professor, and M. HOZAWA, Professor, are with the Institute for Chemical Reaction Science, Tohoku University, Sendai 980, Japan. M. IMAISHI, Professor, is with the Institute for Advanced Materials Study, Kyushu University, Kasuga 816, Japan. S. KITAGAWA, Senior Research Engineer, is with the Japan Space Utilization Promotion Center, Tokyo 169, Japan. Manuscript submitted January 24, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
aspects; i.e., aspect 1 has been examined by References 14 through 16, aspects 1 and 2 by References 17 and 18, aspects 1 and 3 by References 19 through 22, and all of these aspects by References 23 and 24. For instance, El-Kaddah and Szekely[17,18] computed the electromagnetic, flow, and temperature fields in a spherical molten metal drop, and compared the calculated lifting force and average temperature of the drop with the previous experimental results. Zong et al.[22] developed a mathematical model which can predict the shape of the deformable drop as well as the electromagnetic field, and investigated the effects of the processing
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