Measurements of the internal structure of gas-liquid plumes
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INTRODUCTION
G A S injection is widely practiced in the metallurgical industry for converting, refining, temperature and composition homogenization, and inclusion flotation. There has been a great deal of work performed on water models of the various injection processes in order to understand the fluid mechanics associated with gas injection. One of the major achievements of such studies has been the measurement of the liquid velocity in the single-phase region. Furthermore, complementary mathematical models of the turbulent, recirculatory flow in the single-phase regions can account for the observations quite well. The nature of the flow in the two-phase region is not understood in detail, principally because the measurement of gas and liquid velocities and phase fractions is more difficult. Furthermore, the mathematical modeling of turbulent, two-phase flow is at a more rudimentary stage of development. Nevertheless, a detailed description of the two-phase region is necessary to understand the exchanges of momentum, heat, and mass in injection systems. Several techniques have been used to investigate the nature of flow in the two-phase region. Electrical probes (EPs) have been used extensively for the measurement of void fraction and bubble frequency distributions.I~.2.3] Information on bubble rising velocity can also be obtained with a modified probe having double tips aligned in the direction of the bubble rise. 14,s,6~Electrical probes of this type cannot be used to measure the liquid velocity. Velocity measurements have been performed with a variety of techniques, such as cinematographic observation of the motion of tracer particles of the liquid flow field, 17~video flow visualization and laser Doppler anemometry (LDA) measurement of the liquid flow, I8,91and the hot film anemometry of the liquid velocities3 l~ Strictly speaking, the latter two techniques are limited to velocity measurements in liquid phase, unless special precautions are taken to identify the individual phases. Y.Y. SHENG, Postdoctoral Fellow, and G.A. IRONS, Professor and Chairman, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada. Manuscript submitted March 24, 1992. METALLURGICAL TRANSACTIONS B
Nevertheless, efforts have been made to obtain velocity information from inside the two-phase zone. Grevet et al. used LDA to obtain velocity data inside the plume zoneY ] They did not mention any specific procedures for discrimination of the velocity data from the gas and liquid phases, so the measured velocities were a mixture of gas and liquid velocities, probably skewed to the liquid phase. In the work performed by Oeters et al.,tL~ the velocity signals from the gas phase may have been eliminated because the cooling effect caused by bubbles to the hot film is rather weak; as a result, most of their data probably originated from the liquid phase. Anagbo and Brimacombe developed a new approach by measuring the liquid velocity in the single-phase zone with an LDA and measuring th
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