Mixing characteristics of a submerged jet measured using an isokinetic sampling probe
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INTRODUCTION
INJECTION technologies are now applied in various iron and steelmaking processes, and a huge number of research works on gas injection have been reported. However, many of them are concerned with the macroscopic mixing character of gas injected into a vessel or a flow pattern in a reactor. Research on the jet itself is limited. On the other hand, the high-speed gas jet plays an important role in basic oxygen furnace, argon-oxygen decarburization furnace, and in-bath smelting processes which require injection of a large amount of gas into a molten metal, with active mixing of gas and liquid expected in the jet zone. The injected gas initially forms a high-speed jet, then changes to a bubble jet, which has been relatively well investigated. Therefore, the mixing characteristics of high-speed gas jets in liquids near the injection point are important in understanding the metallurgical reactions occurring in the above processes. Since a submerged gas jet essentially forms a two-phase flow, two-phase flow instrumentation is important for characterization measurements. An electroresistivity probe was developed and used to measure the void fraction in gas injection experiments, tl-Sj Although this technique is well developed, measurements near the injection point are relatively limited, m31 Though it is reported that highspeed submerged gas jets contain liquid droplets near the injection point, t6,71 in principle, an electroresistivity probe cannot detect them. Therefore, another method which could directly measure the liquid flow in a jet zone was needed. The isokinetic sampling probe is able to collect directly gas and liquid in a two-phase atomized flow, as well as in a bubbly flow. [8,91 This technique was developed to measure the slip velocity between gas and liquid in pipe flows, and many applications are available in the nuclear reactor engineering field. In the metallurgical field, K. ITO, formerly Research Associate, the Research Institute of Mineral Dressing and Metallurgy, Tohoku University, is Associate Professor, Department of Materials Science and Engineering, Waseda University, Tokyo 169, Japan. S. KOBAYASHI, Associate Professor, and M. TOKUDA, Professor, are with the Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Sendal 980, Japan. Manuscript submitted March 7, 1989. METALLURGICAL TRANSACTIONS B
only the application to submerged jets is detailed, t~~ In this technique, the flow field is divided into two parts by means of flow splitters or a tube inserted into the flow parallel to the flow direction. One portion of the flow is drawn off at a rate such that the velocity of each phase is unchanged by the presence of the probe. In the present study, time-averaged flow properties, and mixing characteristics of a submerged upward gas jet were measured using the isokinetic sampling technique in a water model. A mathematical one-dimensional model using dimensionless slip velocity as a parameter was developed and compared with the observations. II.
EXPERIMENTAL
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