Fluid dynamics of vertical submerged gas jets in liquid metal processing systems
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INTRODUCTION
HIGH productivity
in liquid metal processing systems where gas-metal reactions are important requires the use of efficient gas-liquid contacting techniques. The injection of the gas into the liquid metal as a high speed, submerged gas jet provides efficient contacting because the jet breaks up into a swarm of bubbles with a high surface to volume ratio. In addition, the kinetic energy of the jet contributes to the turbulent mixing so that liquid phase mass transfer rates are accelerated. Submerged gas jets are particularly well suited to metallurgical processes because the breakup of the gas stream takes place some distance from the jet orifice, so that, ideally, the region of high reaction rate can be projected into the center of the metal bath, avoiding the refractory wear and heat loss problems which might be associated with the use of other gas-liquid contacting methods. Because alternative techniques are normally used for lower temperature gas-liquid contacting, the fluid dynamics of submerged gas jets has not been a major subject of research in chemical engineering, and appropriate parameters for scaling and optimization of submerged jet systems have not been determined. Process metallurgists interested in the fundamental behavior of such systems have therefore been obliged to begin their studies with small scale, low temperature transparent models in which the jet behavior can be observed and characterized. Mathematical models of the observed behavior can then be developed and tested in larger scale liquid metal systems. In the present study, high speed submerged gas jets of nitrogen, helium, and argon injected into water have been filmed using a high speed rotating prism camera. The jet behavior has been characterized, and the resulting correlation has been tested in small scale liquid metal systems using an orifice pressure trace technique. II.
EXPERIMENTAL APPARATUS AND PROCEDURE
A. Aqueous Model Experiments Water model experiments were carried out in a rectangular tank, 30 cm by 30 cm by 60 cm deep. The gas jet
M.J. McNALLAN is with the Department of Materials Engineering, University of Illinois at Chicago Circle, Chicago, IL 60680. T.B. KING is with the Department of Materials Science and Engineering, Building 8-106, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted August 30, 1979. METALLURGICALTRANSACTIONS B
issued from a brass nozzle mounted in. the center of the tank and facing vertically upwards. In most experiments the nozzle was 40 cm below the liquid surface. The mass flow of the gas was set at a specified rate and, when the flow pattern in the tank had stabilized, the jet was photographed with a Hycam rotating prism camera operating at 3000 to 5000 frames per second. Illumination was provided by two to four halogen lamps. A total of 44 such films was produced of argon, nitrogen, and helium jets injected through orifices 0.1, 0.2, and 0.4 cm in diameter at volumetric flow rates ranging from 180 to 4600 cm 3 per second at standard temperature and
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