Effect of cross-flow on the frequency of bubble formation from a single-hole nozzle
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I.
INTRODUCTION
IN order to enhance the efficiency of current refining processes accompanied by gas injection, some attempts have been made to produce as small bubbles as possible. This is intended to increase the total interfacial area between bubbles and molten metal. Kawakami et al.[1,2] have investigated the effect of ultrasonic oscillation on the frequency of bubble formation from a top lance or a singlehole bottom nozzle. They observed that the frequency of bubble formation, fB, increased appreciably due to ultrasonic oscillation. However, it is not clear whether the same effect can be expected in a molten metal bath, because the density of molten metal is much higher than that of water and oscillating the nozzle becomes difficult due to the added mass effect. Meanwhile, Tsouris et al.[3,4,5] and Sato et al.[6,7] applied an electrostatic field to a single-hole nozzle to generate smaller bubbles. In a water bath, smaller bubbles were actually produced. Also, in this case, it is not clear whether the electrostatic method is effective in a molten metal bath. Tsuge et al.,[8] Marshall et al.,[9] and Yamamura et al.[10] focused on the possibility for the enhancement of the frequency of bubble formation from an orifice placed in a cross-flow. This possibility is expected because the drag force acting on the side of a gas column issuing from the orifice exit is likely to make the gas column detach from it and, hence, to increase the frequency of bubble formation. Unfortunately, a comprehensive understanding of the bubble formation from a single-hole nozzle or an orifice subjected to the influence of cross-flow is not obtained. Generating bubbles from an orifice settled flush on the wall of metallurgical reactors seems difficult because it is MANABU IGUCHI, Professor, is with the Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Hokkaido, 060-8628, Japan. YUKIO TERAUCHI, Researcher, is with the R&D Division, Heraeus Electro-Nite, Japan Ltd., Osaka, 5660045, Japan. SHIN-ICHIRO YOKOYA, Professor, is with the Department of Mechanical Engineering, Nihon Institute of Technology, MinamiSaitama, 345-8501, Japan. Manuscript submitted January 6, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
practically impossible to induce cross-flow along the wall. In this study, we also focused on the effect of cross-flow on the frequency of bubble formation, fB, from a singlehole nozzle attached to a top lance. The experimental apparatus producing cross-flow is different from that used by Tsuge et al.,[8] Marshall et al.,[9] and Yamamura et al.[10] Empirical correlations of fB were proposed as functions of gas flow rate Qg, cross-flow velocity vu, and the inner diameter of the nozzle, dni. II.
EXPERIMENTAL APPARATUS AND PROCEDURE
Figure 1 shows a schematic of the experimental apparatus. A transparent vessel made of acrylic resin was placed in a water jacket and was rotated with a motor settled below the jacket. The inner diameter D and height H of the vessel were 0.1927 and 0.400 m,
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