Characteristics of round vertical gas bubble jets
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I.
INTRODUCTION
W H E N gas is injected into a liquid, a two-phase jet results. In numerous technical processes gas bubble jets are used to achieve large gas-liquid contact areas or to agitate the liquid. For instance, in steelmaking gas jets are blown into liquid metals in the AOD, OBM, and ladle refining processes. For the design of gas injection systems, knowledge of the main jet parameters and their dependence on the blowing conditions is required, e.g., it is necessary to know the geometrical extension of the bubble jet. Further, local gas concentrations, liquid and gas velocities, and the amount of liquid pumped by the jet are of interest. So far, the experimental data published in the literature are not sufficient as a basis for the layout of a technical system, especially in nonstandard cases like gas injection into liquid metals. In the main section of the present paper, extensive measurements on gas bubble jets are reported, comprising air and helium jets in water as well as nitrogen jets in mercury. The most important parameter is the gas concentration, which is measured with electro-resistivity probes. Bubble frequencies and velocities are also determined. The investigation is limited to vertical round jets injected from below. In the following two sections of the paper correlations between the measured data have been derived. As an important tool to describe bubble jets, entrainment models are discussed. Furthermore, nondimensional representations are developed which may be used for engineering purposes. In the final section of the paper the data on gas concentration, bubble frequency, and gas velocities are combined to obtain values for the bubble size.
II.
PREVIOUS WORK
Gas injection into liquids has been investigated from various points of view, ranging from details of the bubble generation process in the vicinity of the nozzle ~ 7 to the overall hydrodynamic and mass transfer properties of the entire vessel, s-~3 With respect to the gas distribution in the liquid K -H TACKE is with Concast Servme Umon AG, Toe&str 7, CH-8027 Zfirich, Swttzerland, H.-G. SCHUBERT ~s with Max-Planck-Insntut f'tir Eisenforschung, Max-Planck-Str. 1, D-4000 Diisseldorf, D -J WEBER and K. SCHWERDTFEGER are with the Inst,tut fiir Allgemeine Metallurgie, Robert-Koch-Sir 42. D-3392 Clausthal-Zellerfeld. Germany. K -H. Tacke and K. Schwerdtfeger were with Max-Planck-lnstitut fhr Eisenforschung when part of the experiment was carried out Manuscript submitted June 20, 1984. METALLURGICAL TRANSACTIONS B
and associated quantities whmh are treated in the present work, several studies have been carried out. ~4-2~
A. Experimental Investigations Radial profiles of liquid velocity, gas concentration and bubble frequency have been reported only for aqueous systems so far. The radial distribution of these quantities is well represented by the Gaussian function as was shown in a large number of experiments. ~ ~-~~7~ Gas velocities exceed the liquid velocities by a slip velocity/5 ~720 which is equal to the velocity of rise of the b
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