The Influence of Eddy Effect of Coils on Flow and Temperature Fields of Molten Droplet in Electromagnetic Levitation Dev
- PDF / 1,225,548 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 43 Downloads / 180 Views
netic levitation (EML) is a widely used technique in material processing. Materials are levitated in space and avoid direct contacts with containers, which is of vital importance for the study of nucleation and the undercooled liquid metals. In addition, thermophysical properties of molten materials can also be measured by EML technique, such as surface tension, electrical conductivity, viscosity, and thermal conductivity.[1–7] Since Muck[8] first proposed the idea of electromagnetic levitation in 1923, several devices have been designed for positioning and melting materials, among which the TEMPUS unit developed by German scientists is well known for separately controlling levitation process and melting process. Very encouraging results have been gained through several Space Shuttle missions using the TEMPUS unit. There are two sets of electromagnetic coils used for positioning and melting materials, respectively in electromagnetic levitation device. The first one operating at a relatively low load is positioning coils, which is used to levitate the materials. The second set of coils operates at LIN FENG, Ph.D. Student, is with the College of Power Engineering, Chongqing University, Chongqing 400044, P. R. China. WAN-YUAN SHI, Professor, is with the College of Power Engineering, Chongqing University and also with the Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education, Chongqing 400044, P. R. China. Contact e-mail: [email protected] Manuscript submitted December 13, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
a higher load and provides energy to heat the materials. In this way, the heating and positioning processes are controlled independently.[9] Upon that, the undercooling of metals can be realized when the heating coils are shut off. In the EML technique, the magnetic force and absorbed power play an important role. With the holding of magnetic force, the sample could levitate in space and the absorbed power enables it to be heated and melted. Lifting force induced by high-frequency circle current was measured experimentally, but fits well with analytical results only when the sample is far away from coils.[10] The analytical solution of absorbed power of the sample was given by Lohfer through solving the simplified Maxwell equations using Bessel functions.[11] Calculations of lifting force and absorbed power in TEMPUS were carried out by Zong and Szekely using the volume integral method.[12] Beyond that, many works were focused on the fluid flow and the stability of the metal in levitation and melting process. Some simulations and experiments showed that the sample levitated in electromagnetic coils tends to be unstable. When the sample is melted, the electromagnetic force generated by coils together with buoyancy and Marangoni convection drive the internal flow of the sample and the velocity tends to be the value of 10 to 40 cm/s.[13–19] The transition of laminar and turbulent flow was detected experimentally at a Reynolds number of 600.[20] Applying an extra static magnet
Data Loading...
