Numerical Evaluation of Cyclone Application for Impurities Removal from Molten Aluminum
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A cyclone separator is one of the most popular units in the industrial practice of separation or removal of impurities from a gas or liquid. The advantages of the cyclone that make it attractive for industrial application include the absence of moving parts, low operational costs, and design simplicity. Impurities in casting practice are always a crucial issue determining the quality of cast products. Entrapped oxides in the form of films and particles are the most common incidents in the solidified metal.[1] The level of oxides and inclusions in the molten metal in today’s cast house is controlled by filter boxes[2] and degassing units.[3,4] However, the application of such systems, i.e., filter boxes, can be limited. During the transfer of molten metal through these systems, the pick up of earlier removed impurities occurs, leading to the varying efficiency of the filter (i.e., filter aging).[5] Moreover, expensive filters have to be replaced regularly. While the impurities removal from molten metal has remained the important issue for many years, to the best of our knowledge, the application of a cyclone for molten metal processing has rarely been considered until recently.[6,7] The removal of entrained in the molten steel low density particles (alumina) in a cyclone with an axial, cylindrical capture surface has been studied numerically, using commercially available software with incorporated turbulence models by Slack and Wraith.[6] By assuming particle adhesion to the solid core, A.N. TURCHIN, PhD Student, and D.G. ESKIN, Senior Scientist, are with the Netherlands Institute for Metals Research, 2628CD Delft, The Netherlands. L. KATGERMAN, Professor, is with the Department of Materials Science and Engineering, Delft University of Technology, 2628CD Delft, The Netherlands. Contact e-mail: [email protected]. Contact e-mail: [email protected] Manuscript submitted July 11, 2007. Article published online February 20, 2008. 364—VOLUME 39B, APRIL 2008
optimizing the design of the cyclone, and applying the process conditions corresponding to the practical scale, they demonstrated using the Reynolds stress model (RSM) that all particles larger in size than 35 lm and a considerable portion of those between 15 and 30 lm were removed from the stream of molten steel. Later, Zuidema adapted a more conventional cyclone design for alumina removal from the stream of molten aluminum.[7] A series of calculations using the renormalized group model (RNG, k - e) aimed at the efficiency of the cyclone resulted in a patent.[8] However, the results of this work were obtained only for a fixed inlet velocity of 0.01 m/s, which is far less than those commonly occurring in a cast house. In spite of the fact that the operation of hydrocyclones acting mostly with an air core has been sufficiently understood and improved owing to the development of computational fluid dynamics and recent advances in computational power, many questions still remain answered in regards to transferring the cyclone concept to molten metal processing. What are the consequenc
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