Fluid dynamics in bubble stirred ladles: Part I. experiments
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I.
INTRODUCTION
GAS-liquid processes play a very important role in both metallurgical and chemical engineering reactors. Usually it is essential to obtain a large contact area between the two phases. Furthermore, one wishes to avoid "deadwater" regions in the reactor and it is therefore important to describe flow patterns and velocities in the reactor. In chemical engineering processes gas is often introduced through a large number of holes or nozzles in the bottom p l a t e - - a bubble column. In high-temperature processes--due to the refractory problem--only a small number of nozzles or tuyeres are employed. The actual metallurgical reactors, the ladles, are often near-cylindrical (usually a truncated cone) in shape in order to reduce refractory consumption. Simple analytical or numerical models have been used to calculate hold-up and liquid circulation in bubble columns. ~1'2j However, experimental results indicate that such models are applicable only within limited flow regimes and reactor geometries. In high temperature reactors--employing only one or a few nozzles--contact areas could not be calculated with any accuracy and only recently have calculations of mixing times been proposed, t3J During the last decade a number of mathematical models have been described to calculate flows induced by one nozzle or porous plug in a ladle or converter. [4'51 H o w e v e r , due to the crude m e a s u r e m e n t techniques and shortage of data available in the high temperature systems, the published models have not been satisfactorily verified. One exception is the experimental work of Grevet et al.I24j They measured the velocity field in a water model of a cylindrical ladle for two gas flowrates which spanned over a factor of two. Unfortunately, they did not obtain results in the bubbly region, and they did not report the duration of their experiments. The duration of the experiments is a critical factor which has not been given sufficient attention. In a previous work r25[we showed
S.T. JOHANSEN, Research Engineer, is with SINTEF, Division of Metallurgy, N-7034 Trondheim-NTH, Norway. D. G. C. ROBERTSON, formerly a Visiting Scientist at SINTEF, is Professor, Department of Metallurgical Engineering, University of Missouri-Rolla, Foulton Hall, Rolla, MO 65401-0249. K. WOJE, formerly Engineer at SINTEF, is Engineer with Scrco Engineering A/S, Alsteinsgt. 7, P.B. 618, N-4001 Stavanger, Norway. T. A. ENGH is Professor, Department of Metallurgy, the Technical University of Trondheim, N-7034 Trondheim-NTH, Norway. Manuscript submitted July 30, 1986. METALLURGICALTRANSACTIONSB
that in a 1.2 m 2 ladle the flow exhibits fluctuations with very large timescales, ranging from 1 second to several minutes. Hence, it was necessary to measure for a period of 15 minutes at each point to obtain reproducible time averaged results. To allow a more exact verification of the theoretical calculations, we have attempted to make accurate measurements of the flow in a water model of the metallurgical ladle. The influence on the flow patter
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