Effect of Nozzle Diameter on Mixing Time During Bottom-Gas Injection in Metallurgical Ladles
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WATER modeling has been employed for more than 40 years to investigate fluid flow in metallurgical vessels. This technique overcomes the limitation of opacity of liquid metals. In spite of satisfying geometrical, kinematic, and the main dynamic criteria on similitude, water modeling still has several drawbacks. A. Type of Injection Device Bottom gas stirring in industrial metallurgical ladles is carried out with porous plugs, and most water models employ nozzles. Bubble formation in nozzles and porous plugs in gas/water systems is different. Anagbo and Brimacombe[1] reported the bubble size in a water model for a low gas flow rate in the range from 8 to 14 cm3/s per cm2 of porous plug area, indicating a smaller bubble size with porous plugs in comparison with nozzles, 3 to 4 mm and 15 mm, respectively. Above this gas flow rate, incipient bubble coalescence starts to develop and the bubble diameter increases up to 35 to 50 mm. In addition to this, the bubble size in gas/water and gas/ metal systems is also different. There is strong experimental evidence that bubbles in gas/metal systems are significantly larger than in identical gas/water systems.[1– 3] The bubbles in a gas/metal system are bigger because of the nonwetting conditions, and their final volume is dominated by the fluid properties: surface tension (r) and density (q). The ratio r/q is 73 for the air/water system and 251 for the air/steel system. Irons and
M.S.C. TERRAZAS, formerly Graduate Student, Morelia Technological Institute, Av. Tecnolo´gico 1500, Col. Lomas de Santiaguito, 58120 Morelia, Mich, Me´xico, is now EAF/CC Shop Supervisor with the, TyASA, Carretera Federal Me´xico-Veracruz km 321 s/n int.2, 94450 Ixtaczoquitla´n, VER, Me´xico. ALBERTO N. CONEJO, Professor, is with Morelia Technological Institute. Contact e-mails: [email protected]; [email protected] Manuscript submitted August 10, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
Guthrie[2] reported that the nonwetting conditions in a gas/metal system lead to bubble formation at the outer nozzle diameter.[2] Stapurewicz and Themelis[4] investigated mixing time in a large water model using porous plugs and a nozzle with central gas injection. Three different diameters were employed arbitrarily in the experiments. They reported similar results in terms of mixing time as well an improved mass transfer coefficient with porous plugs in comparison with nozzles; however, this effect decreased as the gas flow rate increased. Sahai and Guthrie[5] postulated on theoretical grounds that any hydrodynamic analysis of flow recirculation is not affected by the bubbles formed by either nozzles or porous plugs. Mazumdar and Guthrie[6] also stated in a review paper that the equilibrium distribution bubble size in the fully developed region of the plume is determined by the thermophysical properties of the system and not by the inlet operating variables (gasinjection device, orifice diameter, etc.). Bubbles reach an equilibrium bubble size in the plume region due to the decrease in hydrostatic pressure and
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