Modeling of Ascending/Descending Velocity of Metal Droplet Emulsified in Pb-Salt System
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THE mixing of two immiscible liquids is required in many processes (biodiesel, metal-slag, nuclear reactor, etc.) to increase the efficiency of the process. The mixing can be achieved either by stirring the liquids mechanically or by injecting a gas.[1] In many metallurgical processes (ladle metallurgy, secondary refining, Cu convertor, etc.), the metal-slag reaction is of prime importance to increase the efficiency of the process. Slag and metal are immiscible liquids at high temperature and are in contact only at the interface, which leaves little room for a good rate of reaction between them unless the surface area of one of the phases is increased. The reaction rate, efficiency, and productivity of the process are related to each other. An effective method to increase the area is to emulsify the slag into the metal phase or the metal into the slag phase. The first method is unstable and not desirable.[2] The second is effective. The current work deals with the second method, which is called metal emulsification.[3–7] As shown in Figure 1,
DUK-YONG SONG, Ph.D. Student, is with the Graduate School of Engineering, Tohoku University, 6-6 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan. Contact e-mail: [email protected]. ac.jp NOBUHIRO MARUOKA, Assistant Professor, HIROYUKI SHIBATA, Associate Professor, and SHIN-YA KITAMURA, Professor, are with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan. GOVIND SHARAN GUPTA, Professor, and SMITA KAMBLE, Ph.D. Student, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India. Manuscript submitted January 10, 2012. Article published online March 8, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
the molten metal is placed at the bottom, whereas the slag is placed at the top as it is lighter compared with the metal. A nozzle, placed at the bottom of the metal phase, blows a gas bubble into it. This bubble rises from the metal into the slag phase, and as it does so, it carries with it a metal film into the slag phase. This film then disintegrates in the slag phase to form the metal droplets. The process of metal emulsification can be divided into three stages. The first stage includes the formation and motion of gas bubble in the metal and slag phase. The nozzle blows gas into the metal. The bubble grows until its diameter reaches a critical value,[8,9] at which it starts its upward motion. The bubble rises with its terminal velocity and reaches the interface. From here, the second stage begins (in continuation of the first stage), i.e., the formation of the film and the breakage of the film. As the bubble crosses the interface it drags some lower phase liquid in its wake and forms a film of molten metal around bubble and carries this film into the slag phase. When the bubble crosses the interface completely, a few large metal drops are formed from the dragged phase.[10,11] Bubble with liquid film around it still continues its journey in the slag phase. A
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