Model study of bubble and liquid-flow characteristics in a bottom blown bath under reduced pressure
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I.
INTRODUCTION
RECENTLY, RH (Ruhlstahl-Heraus) and DH (Dortmund H6rder) degassing processes have been used for producing high-purity steel, u~61 In these processes, gas is injected into the bath of the reactor under reduced surface pressures mainly to induce liquid flow and thus promote decarburization, desulfurization, etc. In practical situations, however, quantitative evaluation of refining efficiency at each reaction site is not known clearly.t7.8.gl Fundamental studies of the mixing time and the volumetric mass transfer coefficient between bubble and liquid under reduced pressures, therefore, have been carried out by many researchers. I1,~~ As a result, it is commonly recognized that for further enhancement of the efficiency of these degassing processes, the bubble behavior in a bath and liquid motion induced by rising bubbles should be understood in detail. In this study, at first, we focused on the bubble behavior characterized by gas holdup a, bubble frequency fB, mean bubble rising velocity ~ , and mean chord length L8 in a cylindrical water bath under a reduced surface pressure slightly higher than the vapor pressure at the bath temperature. These parameters can be measured with an electroresistivity probe.t~5-2q Next, the axial and radial mean velocities, the root-mean-square (rms) values of the axial and radial turbulence components, the Reynolds shear
MANABU IGUCHI, Associate Professor, is with the Department of Materials Science and Processing, Faculty of Engineering, Osaka University, Osaka, 565 Japan. HIROSHI UEDA, formerly Graduate Student, Department of Materials Science and Processing, Osaka University, is Researcher, lshikawajima-Harima Heavy Industries, Ltd., Kanagawa, 234 Japan. TOMOYUKI CHIHARA, formerly Graduate Student, Department of Materials Science and Processing, Osaka University, is Researcher, Daido Special Steel Ltd., Aichi, 477 Japan. ZEN-ICHIRO MOR1TA, Professor Emeritus, Department of Materials Science and Processing, Osaka University, is Executive Advisor, Sumitomo Metal Industries Ltd., Hyogo, 660 Japan. Manuscript submitted December 23, 1994. METALLURGICALAND MATERIALSTRANSACTIONS B
stress, and the skewness and flatness factors for the axial and radial turbulence components were Obtained by using a two-dimensional laser Doppler velocimeter. The effects of the reduced pressure on the bubble and liquid-flow characteristics were clarified from a comparison with their respective characteristics for an atmospheric surface pressure. Furthermore, the experimental results of liquid-flow characteristics were compared with those for a single-phase free jet to make clear the difference in turbulence structures between bubbling and single-phase jets. II.
EXPERIMENT
Figure I shows a schematic of the experimental apparatus. Water was filled in a cylindrical acrylic vessel with an inner diameter of 20 cm and a height of 40 cm to a depth of 25 cm. The cylindrical vessel was designed to model primarily the reactors in DH degassing processes/:~ Air was injected into the bath through a cen
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