Large-scale measurements of the physical characteristics of round vertical bubble plumes in liquids
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I.
INTRODUCTION
A L T H O U G H gas injection has been practiced in the steelmaking industry for about 130 years, there is still no complete quantitative understanding of the dynamics of these gas/liquid systems. Consequently, more research is needed to find suitable correlations with which flow velocities, gas fraction, and bubble size can be predicted. In the present work, the behavior of center-injected gas jets in the system air/water has been investigated in pilot scale. One of the goals of this research was to examine whether the correlations for the gas concentration which are available from bench scale experiments are valid in a system of much larger dimension. Another aim was to establish correlations for the velocity of both phases. The dynamic behavior of the system received special attention.
II. GENERAL DESCRIPTION OF GAS STIRRED GAS/LIQUID SYSTEMS When a gas jet is discharged into a liquid at the bottom of a vessel, there are two main flow regimes along its trajectory3 ~ Immediately above the nozzle, there is a transition zone in which the disintegration of the gas stream into bubbles takes place. At some distance upward, the disintegration of the gas stream is completed and the bubble zone becomes fully developed. The bubble zone may be subdivided into a lower region, where the gas still has some of its initial momentum, and into its main part, where the motion of the gas relative to the liquid is buoyancy driven. In terms of physics, the upper part is similar to a one-phase plume driven by density differences and should be called a plume (bubble plume) rather than a jet. The motion of the liquid phase is caused by momentum transfer from the gas jet to the liquid in MARCO A.S.C. CASTELLO-BRANCO, formerly Scientist, Institut fiir Allgerneine Metallurgie, Technical University of Clausthal, is with M a n n e s m a n n S.A., 30,000 Belo Horizonte, Brazil. KLAUS SCHWERDTFEGER, Professor, is with the Institut fiJr Allgemeine Metallurgie, Technical University of Clausthal, 38678 ClausthalZellerfeld, Germany. Manuscript submitted January 22, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
the zone close to the nozzle and by the buoyancy force exerted by the bubbles in the region above. A fundamental feature of bubble plumes in liquids is the fluctuating character, both in time and space, of the plume properties. This means that in the determination of time averages for gas fraction, bubble frequency, and velocity, due consideration has to be given to these fluctuations, and that the methods of statistics may be used for proper design of the experimental program and the analysis of the data. tz 8] III.
E X P E R I M E N T A L TECHNIQUE
The experimental setup is shown schematically in Figure 1. The polypropylene vessel size approximates that of a 30-ton ladle for steel. It is cylindrical and has an ID of 1600 mm and a height of 2250 mm. There is a nozzle adapter at the bottom at the center of the vessel. Cylindrical nozzles made of stainless steel or brass can be inserted into the adapter. The upper end
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