Scaling estimations of thermal and flow field in gas-stirred ladles
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Scaling Estimations of Thermal and Flow Field in Gas-Stirred Ladles SUVANKAR GANGULY and SUMAN CHAKRABORTY To obtain a better understanding of the physical process involved in gas stirring of a steelmaking vessel, a scaling analysis approach is developed that accounts for the effects of natural convection and axisymmetric bottom gas injection in the vessel. The orders of magnitude of some important quantities such as the transient velocity scale, thermal boundary layer thickness, and the critical flow rate to homogenize the thermal stratification in the molten steel are predicted successfully.
Several metallurgical processes involve gas injection into liquid metals contained in a vessel, with a purpose of refinement and homogenization of the system under concern. Typical examples include degassing operations of molten steel by argon injection, desulfurization of steel baths by inert carrier gases, and gas stirring of molten-steel ladles to achieve homogeneous temperature and composition. In all of the preceding situations, exchange of mass, momentum, and heat
SUVANKAR GANGULY, Researcher, is with the Research and Development Division, Tata Steel, Jamshedpur – 831001, India. Contact e-mail: [email protected] SUMAN CHAKRABORTY, Assistant Professor, is with the Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur – 721302, India. Manuscript submitted April 14, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
between injected gas and the liquid metal generates a vigorous advection in the liquid bath. The resultant transport processes have considerable effects on the thermal histories and cooling rates, which, in turn, strongly influence the quality of the final end product.[1] Thus, in order to have a stringent control on the product quality, a fundamental understanding of the fluid-flow and heat-transfer characteristics during the process is extremely important. Over the last few decades, many researchers have been engaged in studying the hydrodynamic phenomena associated with submerged gas injection into liquid metals.[2–20] A majority of the studies in this field have been primarily experimental, typically depicting the physical characteristics of gas-liquid plumes in the context of ladle processing.[2–11] In general, the experimental studies have mostly been carried out using various kinds of transparent aqueous analogues. Several techniques have been used to investigate the nature of flow in the two-phase region in such situations. In most of the experiments, electrical probes have been used extensively for the measurement of void fraction and bubble frequency distributions. Velocity measurements have also been performed with a variety of techniques, such as direct film capturing, hot wire anemometry, and laser Doppler anemometry measurement of the liquid flow.[4,5,6] Krishnamurthy et al.[4] applied a still photographic technique to characterize the geometry of two-phase axisymmetric plumes in a cylindrical vessel, for a wide range of gas flow rates, bath depths, and orifice diameter
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